Adding upstream version 115.7.0esr.upstream/115.7.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

100 files changed, 21186 insertions, 0 deletions

diff --git a/testing/web-platform/tests/streams/META.yml b/testing/web-platform/tests/streams/META.yml
new file mode 100644
index 0000000000..1259a55cb5
--- /dev/null
+++ b/testing/web-platform/tests/streams/META.yml
@@ -0,0 +1,7 @@
+spec: https://streams.spec.whatwg.org/
+suggested_reviewers:
+  - domenic
+  - yutakahirano
+  - youennf
+  - wanderview
+  - ricea
diff --git a/testing/web-platform/tests/streams/README.md b/testing/web-platform/tests/streams/README.md
new file mode 100644
index 0000000000..9ab6e1284a
--- /dev/null
+++ b/testing/web-platform/tests/streams/README.md
@@ -0,0 +1,3 @@
+# Streams Tests
+
+The work on the streams tests is closely tracked by the specification authors, who maintain a reference implementation intended to match the spec line-by-line while passing all of these tests. See [the whatwg/streams repository for details](https://github.com/whatwg/streams/tree/main/reference-implementation). Some tests may be in that repository while the spec sections they test are still undergoing heavy churn.
diff --git a/testing/web-platform/tests/streams/idlharness-shadowrealm.window.js b/testing/web-platform/tests/streams/idlharness-shadowrealm.window.js
new file mode 100644
index 0000000000..099b2475ca
--- /dev/null
+++ b/testing/web-platform/tests/streams/idlharness-shadowrealm.window.js
@@ -0,0 +1,2 @@
+// META: script=/resources/idlharness-shadowrealm.js
+idl_test_shadowrealm(["streams"], ["dom"]);
diff --git a/testing/web-platform/tests/streams/idlharness.any.js b/testing/web-platform/tests/streams/idlharness.any.js
new file mode 100644
index 0000000000..42a17da58c
--- /dev/null
+++ b/testing/web-platform/tests/streams/idlharness.any.js
@@ -0,0 +1,79 @@
+// META: global=window,worker
+// META: script=/resources/WebIDLParser.js
+// META: script=/resources/idlharness.js
+// META: timeout=long
+
+idl_test(
+  ['streams'],
+  ['dom'], // for AbortSignal
+  async idl_array => {
+    // Empty try/catches ensure that if something isn't implemented (e.g., readable byte streams, or writable streams)
+    // the harness still sets things up correctly. Note that the corresponding interface tests will still fail.
+
+    try {
+      new ReadableStream({
+        start(c) {
+          self.readableStreamDefaultController = c;
+        }
+      });
+    } catch {}
+
+    try {
+      new ReadableStream({
+        start(c) {
+          self.readableByteStreamController = c;
+        },
+        type: 'bytes'
+      });
+    } catch {}
+
+    try {
+      let resolvePullCalledPromise;
+      const pullCalledPromise = new Promise(resolve => {
+        resolvePullCalledPromise = resolve;
+      });
+      const stream = new ReadableStream({
+        pull(c) {
+          self.readableStreamByobRequest = c.byobRequest;
+          resolvePullCalledPromise();
+        },
+        type: 'bytes'
+      });
+      const reader = stream.getReader({ mode: 'byob' });
+      reader.read(new Uint8Array(1));
+      await pullCalledPromise;
+    } catch {}
+
+    try {
+      new WritableStream({
+        start(c) {
+          self.writableStreamDefaultController = c;
+        }
+      });
+    } catch {}
+
+    try {
+      new TransformStream({
+        start(c) {
+          self.transformStreamDefaultController = c;
+        }
+      });
+    } catch {}
+
+    idl_array.add_objects({
+      ReadableStream: ["new ReadableStream()"],
+      ReadableStreamDefaultReader: ["(new ReadableStream()).getReader()"],
+      ReadableStreamBYOBReader: ["(new ReadableStream({ type: 'bytes' })).getReader({ mode: 'byob' })"],
+      ReadableStreamDefaultController: ["self.readableStreamDefaultController"],
+      ReadableByteStreamController: ["self.readableByteStreamController"],
+      ReadableStreamBYOBRequest: ["self.readableStreamByobRequest"],
+      WritableStream: ["new WritableStream()"],
+      WritableStreamDefaultWriter: ["(new WritableStream()).getWriter()"],
+      WritableStreamDefaultController: ["self.writableStreamDefaultController"],
+      TransformStream: ["new TransformStream()"],
+      TransformStreamDefaultController: ["self.transformStreamDefaultController"],
+      ByteLengthQueuingStrategy: ["new ByteLengthQueuingStrategy({ highWaterMark: 5 })"],
+      CountQueuingStrategy: ["new CountQueuingStrategy({ highWaterMark: 5 })"]
+    });
+  }
+);
diff --git a/testing/web-platform/tests/streams/piping/abort.any.js b/testing/web-platform/tests/streams/piping/abort.any.js
new file mode 100644
index 0000000000..503de9dcaf
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/abort.any.js
@@ -0,0 +1,408 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+// Tests for the use of pipeTo with AbortSignal.
+// There is some extra complexity to avoid timeouts in environments where abort is not implemented.
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+const errorOnPull = {
+  pull(controller) {
+    // This will cause the test to error if pipeTo abort is not implemented.
+    controller.error('failed to abort');
+  }
+};
+
+// To stop pull() being called immediately when the stream is created, we need to set highWaterMark to 0.
+const hwm0 = { highWaterMark: 0 };
+
+for (const invalidSignal of [null, 'AbortSignal', true, -1, Object.create(AbortSignal.prototype)]) {
+  promise_test(t => {
+    const rs = recordingReadableStream(errorOnPull, hwm0);
+    const ws = recordingWritableStream();
+    return promise_rejects_js(t, TypeError, rs.pipeTo(ws, { signal: invalidSignal }), 'pipeTo should reject')
+        .then(() => {
+          assert_equals(rs.events.length, 0, 'no ReadableStream methods should have been called');
+          assert_equals(ws.events.length, 0, 'no WritableStream methods should have been called');
+        });
+  }, `a signal argument '${invalidSignal}' should cause pipeTo() to reject`);
+}
+
+promise_test(t => {
+  const rs = recordingReadableStream(errorOnPull, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject')
+      .then(() => Promise.all([
+        rs.getReader().closed,
+        promise_rejects_dom(t, 'AbortError', ws.getWriter().closed, 'writer.closed should reject')
+      ]))
+      .then(() => {
+        assert_equals(rs.events.length, 2, 'cancel should have been called');
+        assert_equals(rs.events[0], 'cancel', 'first event should be cancel');
+        assert_equals(rs.events[1].name, 'AbortError', 'the argument to cancel should be an AbortError');
+        assert_equals(rs.events[1].constructor.name, 'DOMException',
+                      'the argument to cancel should be a DOMException');
+      });
+}, 'an aborted signal should cause the writable stream to reject with an AbortError');
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    const rs = recordingReadableStream(errorOnPull, hwm0);
+    const ws = new WritableStream();
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    abortController.abort(reason);
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+    const error = await pipeToPromise.catch(e => e);
+    await rs.getReader().closed;
+    await promise_rejects_exactly(t, error, ws.getWriter().closed, 'the writable should be errored with the same object');
+    assert_equals(signal.reason, error, 'signal.reason should be error'),
+    assert_equals(rs.events.length, 2, 'cancel should have been called');
+    assert_equals(rs.events[0], 'cancel', 'first event should be cancel');
+    assert_equals(rs.events[1], error, 'the readable should be canceled with the same object');
+  }, `(reason: '${reason}') all the error objects should be the same object`);
+}
+
+promise_test(t => {
+  const rs = recordingReadableStream(errorOnPull, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal, preventCancel: true }), 'pipeTo should reject')
+      .then(() => assert_equals(rs.events.length, 0, 'cancel should not be called'));
+}, 'preventCancel should prevent canceling the readable');
+
+promise_test(t => {
+  const rs = new ReadableStream(errorOnPull, hwm0);
+  const ws = recordingWritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal, preventAbort: true }), 'pipeTo should reject')
+      .then(() => {
+        assert_equals(ws.events.length, 0, 'writable should not have been aborted');
+        return ws.getWriter().ready;
+      });
+}, 'preventAbort should prevent aborting the readable');
+
+promise_test(t => {
+  const rs = recordingReadableStream(errorOnPull, hwm0);
+  const ws = recordingWritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal, preventCancel: true, preventAbort: true }),
+                         'pipeTo should reject')
+    .then(() => {
+      assert_equals(rs.events.length, 0, 'cancel should not be called');
+      assert_equals(ws.events.length, 0, 'writable should not have been aborted');
+      return ws.getWriter().ready;
+    });
+}, 'preventCancel and preventAbort should prevent canceling the readable and aborting the readable');
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    const rs = new ReadableStream({
+      start(controller) {
+        controller.enqueue('a');
+        controller.enqueue('b');
+        controller.close();
+      }
+    });
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    const ws = recordingWritableStream({
+      write() {
+        abortController.abort(reason);
+      }
+    });
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+    const error = await pipeToPromise.catch(e => e);
+    assert_equals(signal.reason, error, 'signal.reason should be error');
+    assert_equals(ws.events.length, 4, 'only chunk "a" should have been written');
+    assert_array_equals(ws.events.slice(0, 3), ['write', 'a', 'abort'], 'events should match');
+    assert_equals(ws.events[3], error, 'abort reason should be error');
+  }, `(reason: '${reason}') abort should prevent further reads`);
+}
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    let readController;
+    const rs = new ReadableStream({
+      start(c) {
+        readController = c;
+        c.enqueue('a');
+        c.enqueue('b');
+      }
+    });
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    let resolveWrite;
+    const writePromise = new Promise(resolve => {
+      resolveWrite = resolve;
+    });
+    const ws = recordingWritableStream({
+      write() {
+        return writePromise;
+      }
+    }, new CountQueuingStrategy({ highWaterMark: Infinity }));
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    await delay(0);
+    await abortController.abort(reason);
+    await readController.close(); // Make sure the test terminates when signal is not implemented.
+    await resolveWrite();
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+    const error = await pipeToPromise.catch(e => e);
+    assert_equals(signal.reason, error, 'signal.reason should be error');
+    assert_equals(ws.events.length, 6, 'chunks "a" and "b" should have been written');
+    assert_array_equals(ws.events.slice(0, 5), ['write', 'a', 'write', 'b', 'abort'], 'events should match');
+    assert_equals(ws.events[5], error, 'abort reason should be error');
+  }, `(reason: '${reason}') all pending writes should complete on abort`);
+}
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    },
+    cancel() {
+      return Promise.reject(error1);
+    }
+  }, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'a rejection from underlyingSource.cancel() should be returned by pipeTo()');
+
+promise_test(t => {
+  const rs = new ReadableStream(errorOnPull, hwm0);
+  const ws = new WritableStream({
+    abort() {
+      return Promise.reject(error1);
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'a rejection from underlyingSink.abort() should be returned by pipeTo()');
+
+promise_test(t => {
+  const events = [];
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    },
+    cancel() {
+      events.push('cancel');
+      return Promise.reject(error1);
+    }
+  }, hwm0);
+  const ws = new WritableStream({
+    abort() {
+      events.push('abort');
+      return Promise.reject(error2);
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws, { signal }), 'pipeTo should reject')
+      .then(() => assert_array_equals(events, ['abort', 'cancel'], 'abort() should be called before cancel()'));
+}, 'a rejection from underlyingSink.abort() should be preferred to one from underlyingSource.cancel()');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'abort signal takes priority over closed readable');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'abort signal takes priority over errored readable');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    }
+  }, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  const writer = ws.getWriter();
+  return writer.close().then(() => {
+    writer.releaseLock();
+    return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+  });
+}, 'abort signal takes priority over closed writable');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    }
+  }, hwm0);
+  const ws = new WritableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'abort signal takes priority over errored writable');
+
+promise_test(() => {
+  let readController;
+  const rs = new ReadableStream({
+    start(c) {
+      readController = c;
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventClose: true });
+  readController.close();
+  return Promise.resolve().then(() => {
+    abortController.abort();
+    return pipeToPromise;
+  }).then(() => ws.getWriter().write('this should succeed'));
+}, 'abort should do nothing after the readable is closed');
+
+promise_test(t => {
+  let readController;
+  const rs = new ReadableStream({
+    start(c) {
+      readController = c;
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventAbort: true });
+  readController.error(error1);
+  return Promise.resolve().then(() => {
+    abortController.abort();
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => ws.getWriter().write('this should succeed'));
+}, 'abort should do nothing after the readable is errored');
+
+promise_test(t => {
+  let readController;
+  const rs = new ReadableStream({
+    start(c) {
+      readController = c;
+    }
+  });
+  let resolveWrite;
+  const writePromise = new Promise(resolve => {
+    resolveWrite = resolve;
+  });
+  const ws = new WritableStream({
+    write() {
+      readController.error(error1);
+      return writePromise;
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventAbort: true });
+  readController.enqueue('a');
+  return delay(0).then(() => {
+    abortController.abort();
+    resolveWrite();
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => ws.getWriter().write('this should succeed'));
+}, 'abort should do nothing after the readable is errored, even with pending writes');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    pull(controller) {
+      return delay(0).then(() => controller.close());
+    }
+  });
+  let writeController;
+  const ws = new WritableStream({
+    start(c) {
+      writeController = c;
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventCancel: true });
+  return Promise.resolve().then(() => {
+    writeController.error(error1);
+    return Promise.resolve();
+  }).then(() => {
+    abortController.abort();
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => {
+    assert_array_equals(rs.events, ['pull'], 'cancel should not have been called');
+  });
+}, 'abort should do nothing after the writable is errored');
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    pull(c) {
+      c.enqueue(new Uint8Array([]));
+    },
+    type: "bytes",
+  });
+  const ws = new WritableStream();
+  const [first, second] = rs.tee();
+
+  let aborted = false;
+  first.pipeTo(ws, { signal: AbortSignal.abort() }).catch(() => {
+    aborted = true;
+  });
+  await delay(0);
+  assert_true(!aborted, "pipeTo should not resolve yet");
+  await second.cancel();
+  await delay(0);
+  assert_true(aborted, "pipeTo should be aborted now");
+}, "pipeTo on a teed readable byte stream should only be aborted when both branches are aborted");
diff --git a/testing/web-platform/tests/streams/piping/close-propagation-backward.any.js b/testing/web-platform/tests/streams/piping/close-propagation-backward.any.js
new file mode 100644
index 0000000000..5ea47ab85c
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/close-propagation-backward.any.js
@@ -0,0 +1,153 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return rs.pipeTo(ws).then(
+    () => assert_unreached('the promise must not fulfill'),
+    err => {
+      assert_equals(err.name, 'TypeError', 'the promise must reject with a TypeError');
+
+      assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+      assert_array_equals(ws.events, ['close']);
+
+      return Promise.all([
+        rs.getReader().closed,
+        ws.getWriter().closed
+      ]);
+    }
+  );
+
+}, 'Closing must be propagated backward: starts closed; preventCancel omitted; fulfilled cancel promise');
+
+promise_test(t => {
+
+  // Our recording streams do not deal well with errors generated by the system, so give them some help
+  let recordedError;
+  const rs = recordingReadableStream({
+    cancel(cancelErr) {
+      recordedError = cancelErr;
+      throw error1;
+    }
+  });
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_equals(recordedError.name, 'TypeError', 'the cancel reason must be a TypeError');
+
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', recordedError]);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated backward: starts closed; preventCancel omitted; rejected cancel promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(() => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream();
+    const writer = ws.getWriter();
+    writer.close();
+    writer.releaseLock();
+
+    return rs.pipeTo(ws, { preventCancel: falsy }).then(
+      () => assert_unreached('the promise must not fulfill'),
+      err => {
+        assert_equals(err.name, 'TypeError', 'the promise must reject with a TypeError');
+
+        assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+        assert_array_equals(ws.events, ['close']);
+
+        return Promise.all([
+          rs.getReader().closed,
+          ws.getWriter().closed
+        ]);
+      }
+    );
+
+  }, `Closing must be propagated backward: starts closed; preventCancel = ${stringVersion} (falsy); fulfilled cancel ` +
+     `promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream();
+    const writer = ws.getWriter();
+    writer.close();
+    writer.releaseLock();
+
+    return promise_rejects_js(t, TypeError, rs.pipeTo(ws, { preventCancel: truthy })).then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return ws.getWriter().closed;
+    });
+
+  }, `Closing must be propagated backward: starts closed; preventCancel = ${String(truthy)} (truthy)`);
+}
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws, { preventCancel: true, preventAbort: true }))
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return ws.getWriter().closed;
+    });
+
+}, 'Closing must be propagated backward: starts closed; preventCancel = true, preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_js(t, TypeError,
+                         rs.pipeTo(ws, { preventCancel: true, preventAbort: true, preventClose: true }))
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return ws.getWriter().closed;
+  });
+
+}, 'Closing must be propagated backward: starts closed; preventCancel = true, preventAbort = true, preventClose ' +
+   '= true');
diff --git a/testing/web-platform/tests/streams/piping/close-propagation-forward.any.js b/testing/web-platform/tests/streams/piping/close-propagation-forward.any.js
new file mode 100644
index 0000000000..71b6e26284
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/close-propagation-forward.any.js
@@ -0,0 +1,589 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return rs.pipeTo(ws).then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose omitted; rejected close promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(() => {
+
+    const rs = recordingReadableStream({
+      start(controller) {
+        controller.close();
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return rs.pipeTo(ws, { preventClose: falsy }).then(value => {
+      assert_equals(value, undefined, 'the promise must fulfill with undefined');
+    })
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return Promise.all([
+        rs.getReader().closed,
+        ws.getWriter().closed
+      ]);
+    });
+
+  }, `Closing must be propagated forward: starts closed; preventClose = ${stringVersion} (falsy); fulfilled close ` +
+     `promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(() => {
+
+    const rs = recordingReadableStream({
+      start(controller) {
+        controller.close();
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return rs.pipeTo(ws, { preventClose: truthy }).then(value => {
+      assert_equals(value, undefined, 'the promise must fulfill with undefined');
+    })
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, []);
+
+      return rs.getReader().closed;
+    });
+
+  }, `Closing must be propagated forward: starts closed; preventClose = ${String(truthy)} (truthy)`);
+}
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return rs.pipeTo(ws, { preventClose: true, preventAbort: true }).then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose = true, preventAbort = true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return rs.pipeTo(ws, { preventClose: true, preventAbort: true, preventCancel: true }).then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose = true, preventAbort = true, preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws);
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; preventClose omitted; rejected close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws, { preventClose: true });
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = rs.pipeTo(ws);
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; dest never desires chunks; ' +
+   'preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; dest never desires chunks; ' +
+   'preventClose omitted; rejected close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = rs.pipeTo(ws, { preventClose: true });
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; dest never desires chunks; ' +
+   'preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws);
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.close());
+  }, 10);
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed after one chunk; preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.close());
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed after one chunk; preventClose omitted; rejected close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws, { preventClose: true });
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.close());
+  }, 10);
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: becomes closed after one chunk; preventClose = true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.close();
+
+  // Flush async events and verify that no shutdown occurs.
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'close'
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+
+    return pipePromise.then(() => {
+      assert_array_equals(ws.events, ['write', 'a', 'close']);
+    });
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws, { preventClose: true }).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.close();
+
+  // Flush async events and verify that no shutdown occurs.
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the chunk must have been written, but close must not have happened');
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the chunk must have been written, but close must not have happened');
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes; preventClose = true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but close must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.close();
+    resolveWritePromise();
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but close must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close'],
+      'all chunks must have been written and close must have happened');
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes; becomes closed after first write');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws, { preventClose: true }).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but close must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.close();
+    resolveWritePromise();
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but close must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'all chunks must have been written, but close must not have happened');
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes; becomes closed after first write; preventClose = true');
+
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.close();
+    }
+  });
+  let rejectWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise((resolve, reject) => {
+        rejectWritePromise = reject;
+      });
+    }
+  }, { highWaterMark: 3 });
+  const pipeToPromise = rs.pipeTo(ws);
+  return delay(0).then(() => {
+    rejectWritePromise(error1);
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['write', 'a']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed, 'ws should be errored')
+    ]);
+  });
+}, 'Closing must be propagated forward: erroring the writable while flushing pending writes should error pipeTo');
diff --git a/testing/web-platform/tests/streams/piping/error-propagation-backward.any.js b/testing/web-platform/tests/streams/piping/error-propagation-backward.any.js
new file mode 100644
index 0000000000..ec74592f86
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/error-propagation-backward.any.js
@@ -0,0 +1,630 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+const error2 = new Error('error2!');
+error2.name = 'error2';
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+      assert_array_equals(ws.events, []);
+    });
+
+}, 'Errors must be propagated backward: starts errored; preventCancel omitted; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the write error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write; preventCancel omitted; ' +
+   'fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write; preventCancel omitted; rejected ' +
+   'cancel promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(t => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream({
+      write() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const writer = ws.getWriter();
+
+    return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+      .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+      .then(() => {
+        writer.releaseLock();
+
+        return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: falsy }),
+                               'pipeTo must reject with the write error')
+          .then(() => {
+            assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+            assert_array_equals(ws.events, ['write', 'Hello']);
+          });
+      });
+
+  }, `Errors must be propagated backward: becomes errored before piping due to write; preventCancel = ` +
+     `${stringVersion} (falsy); fulfilled cancel promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream({
+      write() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const writer = ws.getWriter();
+
+    return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+      .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+      .then(() => {
+        writer.releaseLock();
+
+        return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: truthy }),
+                               'pipeTo must reject with the write error')
+          .then(() => {
+            assert_array_equals(rs.eventsWithoutPulls, []);
+            assert_array_equals(ws.events, ['write', 'Hello']);
+          });
+      });
+
+  }, `Errors must be propagated backward: becomes errored before piping due to write; preventCancel = ` +
+     `${String(truthy)} (truthy)`);
+}
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true, preventAbort: true }),
+                             'pipeTo must reject with the write error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, []);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write, preventCancel = true; ' +
+   'preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true, preventAbort: true, preventClose: true }),
+                             'pipeTo must reject with the write error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, []);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write; preventCancel = true, ' +
+   'preventAbort = true, preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('Hello');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write; preventCancel omitted; fulfilled ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('Hello');
+    },
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write; preventCancel omitted; rejected ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('Hello');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }), 'pipeTo must reject with the same error')
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length > 2) {
+        return delay(0).then(() => {
+          throw error1;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write, but async; preventCancel = ' +
+   'false; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    },
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length > 2) {
+        return delay(0).then(() => {
+          throw error1;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write, but async; preventCancel = ' +
+   'false; rejected cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length > 2) {
+        return delay(0).then(() => {
+          throw error1;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }), 'pipeTo must reject with the same error')
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write, but async; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; preventCancel omitted; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; preventCancel omitted; rejected cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write(chunk) {
+      if (chunk === 'c') {
+        return Promise.reject(error1);
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping due to last write; source is closed; ' +
+   'preventCancel omitted (but cancel is never called)');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write(chunk) {
+      if (chunk === 'c') {
+        return Promise.reject(error1);
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }), 'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c']);
+    });
+
+}, 'Errors must be propagated backward: becomes errored after piping due to last write; source is closed; ' +
+   'preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; dest never desires chunks; preventCancel = ' +
+   'false; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; dest never desires chunks; preventCancel = ' +
+   'false; rejected cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; dest never desires chunks; preventCancel = ' +
+   'true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  ws.abort(error1);
+
+  return rs.pipeTo(ws).then(
+    () => assert_unreached('the promise must not fulfill'),
+    err => {
+      assert_equals(err, error1, 'the promise must reject with error1');
+
+      assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+      assert_array_equals(ws.events, ['abort', error1]);
+    }
+  );
+
+}, 'Errors must be propagated backward: becomes errored before piping via abort; preventCancel omitted; fulfilled ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  ws.abort(error1);
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error')
+    .then(() => {
+      return ws.getWriter().closed.then(
+        () => assert_unreached('the promise must not fulfill'),
+        err => {
+          assert_equals(err, error1, 'the promise must reject with error1');
+
+          assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+          assert_array_equals(ws.events, ['abort', error1]);
+        }
+      );
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping via abort; preventCancel omitted; rejected ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  ws.abort(error1);
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true })).then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated backward: becomes errored before piping via abort; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+      return flushAsyncEvents();
+    }
+  });
+
+  const pipePromise = rs.pipeTo(ws);
+
+  rs.controller.enqueue('a');
+
+  return writeCalledPromise.then(() => {
+    ws.controller.error(error1);
+
+    return promise_rejects_exactly(t, error1, pipePromise);
+  }).then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'a']);
+  });
+
+}, 'Errors must be propagated backward: erroring via the controller errors once pending write completes');
diff --git a/testing/web-platform/tests/streams/piping/error-propagation-forward.any.js b/testing/web-platform/tests/streams/piping/error-propagation-forward.any.js
new file mode 100644
index 0000000000..482da2f8a8
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/error-propagation-forward.any.js
@@ -0,0 +1,569 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+const error2 = new Error('error2!');
+error2.name = 'error2';
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['abort', error1]);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  });
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['abort', error1]);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = false; rejected abort promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(t => {
+
+    const rs = recordingReadableStream({
+      start() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: falsy }), 'pipeTo must reject with the same error')
+      .then(() => {
+        assert_array_equals(rs.events, []);
+        assert_array_equals(ws.events, ['abort', error1]);
+      });
+
+  }, `Errors must be propagated forward: starts errored; preventAbort = ${stringVersion} (falsy); fulfilled abort ` +
+     `promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream({
+      start() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: truthy }),
+      'pipeTo must reject with the same error')
+      .then(() => {
+        assert_array_equals(rs.events, []);
+        assert_array_equals(ws.events, []);
+      });
+
+  }, `Errors must be propagated forward: starts errored; preventAbort = ${String(truthy)} (truthy)`);
+}
+
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true, preventCancel: true }),
+    'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, []);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = true, preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true, preventCancel: true, preventClose: true }),
+    'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, []);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = true, preventCancel = true, preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; dest never desires chunks; ' +
+   'preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; dest never desires chunks; ' +
+   'preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; dest never desires chunks; ' +
+   'preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; dest never desires chunks; ' +
+   'preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; dest never desires chunks; ' +
+   'preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; dest never desires chunks; ' +
+   'preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws)).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+
+  return writeCalledPromise.then(() => {
+    rs.controller.error(error1);
+
+    // Flush async events and verify that no shutdown occurs.
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'abort'
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+
+    return pipePromise.then(() => {
+      assert_array_equals(ws.events, ['write', 'a', 'abort', error1]);
+    });
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true })).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+
+  return writeCalledPromise.then(() => {
+    rs.controller.error(error1);
+
+    // Flush async events and verify that no shutdown occurs.
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'abort'
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'abort'
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes; preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws)).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but abort must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.error(error1);
+    resolveWritePromise();
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but abort must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'abort', error1],
+      'all chunks must have been written and abort must have happened');
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes; becomes errored after first write');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true })).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but abort must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.error(error1);
+    resolveWritePromise();
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but abort must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'all chunks must have been written, but abort must not have happened');
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes; becomes errored after first write; preventAbort = true');
diff --git a/testing/web-platform/tests/streams/piping/flow-control.any.js b/testing/web-platform/tests/streams/piping/flow-control.any.js
new file mode 100644
index 0000000000..09c4420f87
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/flow-control.any.js
@@ -0,0 +1,297 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = rs.pipeTo(ws, { preventCancel: true });
+
+  // Wait and make sure it doesn't do any reading.
+  return flushAsyncEvents().then(() => {
+    ws.controller.error(error1);
+  })
+  .then(() => promise_rejects_exactly(t, error1, pipePromise, 'pipeTo must reject with the same error'))
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  })
+  .then(() => readableStreamToArray(rs))
+  .then(chunksNotPreviouslyRead => {
+    assert_array_equals(chunksNotPreviouslyRead, ['a', 'b']);
+  });
+
+}, 'Piping from a non-empty ReadableStream into a WritableStream that does not desire chunks');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('b');
+      controller.close();
+    }
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      if (!resolveWritePromise) {
+        // first write
+        return new Promise(resolve => {
+          resolveWritePromise = resolve;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  const writer = ws.getWriter();
+  const firstWritePromise = writer.write('a');
+  assert_equals(writer.desiredSize, 0, 'after writing the writer\'s desiredSize must be 0');
+  writer.releaseLock();
+
+  // firstWritePromise won't settle until we call resolveWritePromise.
+
+  const pipePromise = rs.pipeTo(ws);
+
+  return flushAsyncEvents().then(() => resolveWritePromise())
+    .then(() => Promise.all([firstWritePromise, pipePromise]))
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close']);
+    });
+
+}, 'Piping from a non-empty ReadableStream into a WritableStream that does not desire chunks, but then does');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      if (!resolveWritePromise) {
+        // first write
+        return new Promise(resolve => {
+          resolveWritePromise = resolve;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  const writer = ws.getWriter();
+  writer.write('a');
+
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a']);
+    assert_equals(writer.desiredSize, 0, 'after writing the writer\'s desiredSize must be 0');
+    writer.releaseLock();
+
+    const pipePromise = rs.pipeTo(ws);
+
+    rs.controller.enqueue('b');
+    resolveWritePromise();
+    rs.controller.close();
+
+    return pipePromise.then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close']);
+    });
+  });
+
+}, 'Piping from an empty ReadableStream into a WritableStream that does not desire chunks, but then the readable ' +
+   'stream becomes non-empty and the writable stream starts desiring chunks');
+
+promise_test(() => {
+  const unreadChunks = ['b', 'c', 'd'];
+
+  const rs = recordingReadableStream({
+    pull(controller) {
+      controller.enqueue(unreadChunks.shift());
+      if (unreadChunks.length === 0) {
+        controller.close();
+      }
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      if (!resolveWritePromise) {
+        // first write
+        return new Promise(resolve => {
+          resolveWritePromise = resolve;
+        });
+      }
+      return undefined;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 3 }));
+
+  const writer = ws.getWriter();
+  const firstWritePromise = writer.write('a');
+  assert_equals(writer.desiredSize, 2, 'after writing the writer\'s desiredSize must be 2');
+  writer.releaseLock();
+
+  // firstWritePromise won't settle until we call resolveWritePromise.
+
+  const pipePromise = rs.pipeTo(ws);
+
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a']);
+    assert_equals(unreadChunks.length, 1, 'chunks should continue to be enqueued until the HWM is reached');
+  }).then(() => resolveWritePromise())
+    .then(() => Promise.all([firstWritePromise, pipePromise]))
+    .then(() => {
+      assert_array_equals(rs.events, ['pull', 'pull', 'pull']);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b','write', 'c','write', 'd', 'close']);
+    });
+
+}, 'Piping from a ReadableStream to a WritableStream that desires more chunks before finishing with previous ones');
+
+class StepTracker {
+  constructor() {
+    this.waiters = [];
+    this.wakers = [];
+  }
+
+  // Returns promise which resolves when step `n` is reached. Also schedules step n + 1 to happen shortly after the
+  // promise is resolved.
+  waitThenAdvance(n) {
+    if (this.waiters[n] === undefined) {
+      this.waiters[n] = new Promise(resolve => {
+        this.wakers[n] = resolve;
+      });
+      this.waiters[n]
+          .then(() => flushAsyncEvents())
+          .then(() => {
+            if (this.wakers[n + 1] !== undefined) {
+              this.wakers[n + 1]();
+            }
+          });
+    }
+    if (n == 0) {
+      this.wakers[0]();
+    }
+    return this.waiters[n];
+  }
+}
+
+promise_test(() => {
+  const steps = new StepTracker();
+  const desiredSizes = [];
+  const rs = recordingReadableStream({
+    start(controller) {
+      steps.waitThenAdvance(1).then(() => enqueue('a'));
+      steps.waitThenAdvance(3).then(() => enqueue('b'));
+      steps.waitThenAdvance(5).then(() => enqueue('c'));
+      steps.waitThenAdvance(7).then(() => enqueue('d'));
+      steps.waitThenAdvance(11).then(() => controller.close());
+
+      function enqueue(chunk) {
+        controller.enqueue(chunk);
+        desiredSizes.push(controller.desiredSize);
+      }
+    }
+  });
+
+  const chunksFinishedWriting = [];
+  const writableStartPromise = Promise.resolve();
+  let writeCalled = false;
+  const ws = recordingWritableStream({
+    start() {
+      return writableStartPromise;
+    },
+    write(chunk) {
+      const waitForStep = writeCalled ? 12 : 9;
+      writeCalled = true;
+      return steps.waitThenAdvance(waitForStep).then(() => {
+        chunksFinishedWriting.push(chunk);
+      });
+    }
+  });
+
+  return writableStartPromise.then(() => {
+    const pipePromise = rs.pipeTo(ws);
+    steps.waitThenAdvance(0);
+
+    return Promise.all([
+      steps.waitThenAdvance(2).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 2, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 2, one chunk must have been written');
+
+        // When 'a' (the very first chunk) was enqueued, it was immediately used to fulfill the outstanding read request
+        // promise, leaving the queue empty.
+        assert_array_equals(desiredSizes, [1],
+                            'at step 2, the desiredSize at the last enqueue (step 1) must have been 1');
+        assert_equals(rs.controller.desiredSize, 1, 'at step 2, the current desiredSize must be 1');
+      }),
+
+      steps.waitThenAdvance(4).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 4, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 4, one chunk must have been written');
+
+        // When 'b' was enqueued at step 3, the queue was also empty, since immediately after enqueuing 'a' at
+        // step 1, it was dequeued in order to fulfill the read() call that was made at step 0. Thus the queue
+        // had size 1 (thus desiredSize of 0).
+        assert_array_equals(desiredSizes, [1, 0],
+                            'at step 4, the desiredSize at the last enqueue (step 3) must have been 0');
+        assert_equals(rs.controller.desiredSize, 0, 'at step 4, the current desiredSize must be 0');
+      }),
+
+      steps.waitThenAdvance(6).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 6, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 6, one chunk must have been written');
+
+        // When 'c' was enqueued at step 5, the queue was not empty; it had 'b' in it, since 'b' will not be read until
+        // the first write completes at step 9. Thus, the queue size is 2 after enqueuing 'c', giving a desiredSize of
+        // -1.
+        assert_array_equals(desiredSizes, [1, 0, -1],
+                            'at step 6, the desiredSize at the last enqueue (step 5) must have been -1');
+        assert_equals(rs.controller.desiredSize, -1, 'at step 6, the current desiredSize must be -1');
+      }),
+
+      steps.waitThenAdvance(8).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 8, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 8, one chunk must have been written');
+
+        // When 'd' was enqueued at step 7, the situation is the same as before, leading to a queue containing 'b', 'c',
+        // and 'd'.
+        assert_array_equals(desiredSizes, [1, 0, -1, -2],
+                            'at step 8, the desiredSize at the last enqueue (step 7) must have been -2');
+        assert_equals(rs.controller.desiredSize, -2, 'at step 8, the current desiredSize must be -2');
+      }),
+
+      steps.waitThenAdvance(10).then(() => {
+        assert_array_equals(chunksFinishedWriting, ['a'], 'at step 10, one chunk must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+                            'at step 10, two chunks must have been written');
+
+        assert_equals(rs.controller.desiredSize, -1, 'at step 10, the current desiredSize must be -1');
+      }),
+
+      pipePromise.then(() => {
+        assert_array_equals(desiredSizes, [1, 0, -1, -2], 'backpressure must have been exerted at the source');
+        assert_array_equals(chunksFinishedWriting, ['a', 'b', 'c', 'd'], 'all chunks finished writing');
+
+        assert_array_equals(rs.eventsWithoutPulls, [], 'nothing unexpected should happen to the ReadableStream');
+        assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c', 'write', 'd', 'close'],
+                            'all chunks were written (and the WritableStream closed)');
+      })
+    ]);
+  });
+}, 'Piping to a WritableStream that does not consume the writes fast enough exerts backpressure on the ReadableStream');
diff --git a/testing/web-platform/tests/streams/piping/general.any.js b/testing/web-platform/tests/streams/piping/general.any.js
new file mode 100644
index 0000000000..faeb8e321a
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/general.any.js
@@ -0,0 +1,224 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+test(() => {
+
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+
+  assert_false(rs.locked, 'sanity check: the ReadableStream must not start locked');
+  assert_false(ws.locked, 'sanity check: the WritableStream must not start locked');
+
+  rs.pipeTo(ws);
+
+  assert_true(rs.locked, 'the ReadableStream must become locked');
+  assert_true(ws.locked, 'the WritableStream must become locked');
+
+}, 'Piping must lock both the ReadableStream and WritableStream');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const ws = new WritableStream();
+
+  return rs.pipeTo(ws).then(() => {
+    assert_false(rs.locked, 'the ReadableStream must become unlocked');
+    assert_false(ws.locked, 'the WritableStream must become unlocked');
+  });
+
+}, 'Piping finishing must unlock both the ReadableStream and WritableStream');
+
+promise_test(t => {
+
+  const fakeRS = Object.create(ReadableStream.prototype);
+  const ws = new WritableStream();
+
+  return methodRejects(t, ReadableStream.prototype, 'pipeTo', fakeRS, [ws]);
+
+}, 'pipeTo must check the brand of its ReadableStream this value');
+
+promise_test(t => {
+
+  const rs = new ReadableStream();
+  const fakeWS = Object.create(WritableStream.prototype);
+
+  return methodRejects(t, ReadableStream.prototype, 'pipeTo', rs, [fakeWS]);
+
+}, 'pipeTo must check the brand of its WritableStream argument');
+
+promise_test(t => {
+
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+
+  rs.getReader();
+
+  assert_true(rs.locked, 'sanity check: the ReadableStream starts locked');
+  assert_false(ws.locked, 'sanity check: the WritableStream does not start locked');
+
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws)).then(() => {
+    assert_false(ws.locked, 'the WritableStream must still be unlocked');
+  });
+
+}, 'pipeTo must fail if the ReadableStream is locked, and not lock the WritableStream');
+
+promise_test(t => {
+
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+
+  ws.getWriter();
+
+  assert_false(rs.locked, 'sanity check: the ReadableStream does not start locked');
+  assert_true(ws.locked, 'sanity check: the WritableStream starts locked');
+
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws)).then(() => {
+    assert_false(rs.locked, 'the ReadableStream must still be unlocked');
+  });
+
+}, 'pipeTo must fail if the WritableStream is locked, and not lock the ReadableStream');
+
+promise_test(() => {
+
+  const CHUNKS = 10;
+
+  const rs = new ReadableStream({
+    start(c) {
+      for (let i = 0; i < CHUNKS; ++i) {
+        c.enqueue(i);
+      }
+      c.close();
+    }
+  });
+
+  const written = [];
+  const ws = new WritableStream({
+    write(chunk) {
+      written.push(chunk);
+    },
+    close() {
+      written.push('closed');
+    }
+  }, new CountQueuingStrategy({ highWaterMark: CHUNKS }));
+
+  return rs.pipeTo(ws).then(() => {
+    const targetValues = [];
+    for (let i = 0; i < CHUNKS; ++i) {
+      targetValues.push(i);
+    }
+    targetValues.push('closed');
+
+    assert_array_equals(written, targetValues, 'the correct values must be written');
+
+    // Ensure both readable and writable are closed by the time the pipe finishes.
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+  // NOTE: no requirement on *when* the pipe finishes; that is left to implementations.
+
+}, 'Piping from a ReadableStream from which lots of chunks are synchronously readable');
+
+promise_test(t => {
+
+  let controller;
+  const rs = recordingReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws).then(() => {
+    assert_array_equals(ws.events, ['write', 'Hello', 'close']);
+  });
+
+  t.step_timeout(() => {
+    controller.enqueue('Hello');
+    t.step_timeout(() => controller.close(), 10);
+  }, 10);
+
+  return pipePromise;
+
+}, 'Piping from a ReadableStream for which a chunk becomes asynchronously readable after the pipeTo');
+
+for (const preventAbort of [true, false]) {
+  promise_test(() => {
+
+    const rs = new ReadableStream({
+      pull() {
+        return Promise.reject(undefined);
+      }
+    });
+
+    return rs.pipeTo(new WritableStream(), { preventAbort }).then(
+        () => assert_unreached('pipeTo promise should be rejected'),
+        value => assert_equals(value, undefined, 'rejection value should be undefined'));
+
+  }, `an undefined rejection from pull should cause pipeTo() to reject when preventAbort is ${preventAbort}`);
+}
+
+for (const preventCancel of [true, false]) {
+  promise_test(() => {
+
+    const rs = new ReadableStream({
+      pull(controller) {
+        controller.enqueue(0);
+      }
+    });
+
+    const ws = new WritableStream({
+      write() {
+        return Promise.reject(undefined);
+      }
+    });
+
+    return rs.pipeTo(ws, { preventCancel }).then(
+         () => assert_unreached('pipeTo promise should be rejected'),
+        value => assert_equals(value, undefined, 'rejection value should be undefined'));
+
+  }, `an undefined rejection from write should cause pipeTo() to reject when preventCancel is ${preventCancel}`);
+}
+
+promise_test(t => {
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws, {
+    get preventAbort() {
+      ws.getWriter();
+    }
+  }), 'pipeTo should reject');
+}, 'pipeTo() should reject if an option getter grabs a writer');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const ws = new WritableStream();
+
+  return rs.pipeTo(ws, null);
+}, 'pipeTo() promise should resolve if null is passed');
+
+promise_test(async t => {
+  /** @type {ReadableStreamDefaultController} */
+  var con;
+  let synchronous = false;
+  new ReadableStream({ start(c) { con = c }}, { highWaterMark: 0 }).pipeTo(
+    new WritableStream({ write() { synchronous = true; } })
+  )
+  // wait until start algorithm finishes
+  await Promise.resolve();
+  con.enqueue();
+  assert_false(synchronous, 'write algorithm must not run synchronously');
+}, "enqueue() must not synchronously call write algorithm");
diff --git a/testing/web-platform/tests/streams/piping/multiple-propagation.any.js b/testing/web-platform/tests/streams/piping/multiple-propagation.any.js
new file mode 100644
index 0000000000..a78652fc06
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/multiple-propagation.any.js
@@ -0,0 +1,227 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+const error2 = new Error('error2!');
+error2.name = 'error2';
+
+function createErroredWritableStream(t) {
+  return Promise.resolve().then(() => {
+    const ws = recordingWritableStream({
+      start(c) {
+        c.error(error2);
+      }
+    });
+
+    const writer = ws.getWriter();
+    return promise_rejects_exactly(t, error2, writer.closed, 'the writable stream must be errored with error2')
+        .then(() => {
+          writer.releaseLock();
+          assert_array_equals(ws.events, []);
+          return ws;
+        });
+  });
+}
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream({
+    start(c) {
+      c.error(error2);
+    }
+  });
+
+  // Trying to abort a stream that is erroring will give the writable's error
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the writable stream\'s error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+      promise_rejects_exactly(t, error2, ws.getWriter().closed, 'the writable stream must be errored with error2')
+    ]);
+  });
+
+}, 'Piping from an errored readable stream to an erroring writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+
+  return createErroredWritableStream(t)
+      .then(ws => promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the readable stream\'s error'))
+      .then(() => {
+        assert_array_equals(rs.events, []);
+
+        return promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1');
+      });
+}, 'Piping from an errored readable stream to an errored writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream({
+    start(c) {
+      c.error(error2);
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+    'pipeTo must reject with the readable stream\'s error')
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+      promise_rejects_exactly(t, error2, ws.getWriter().closed, 'the writable stream must be errored with error2')
+    ]);
+  });
+
+}, 'Piping from an errored readable stream to an erroring writable stream; preventAbort = true');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  return createErroredWritableStream(t)
+  .then(ws => promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                      'pipeTo must reject with the readable stream\'s error'))
+  .then(() => {
+    assert_array_equals(rs.events, []);
+
+    return promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1');
+  });
+
+}, 'Piping from an errored readable stream to an errored writable stream; preventAbort = true');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  const closePromise = writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the readable stream\'s error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+      promise_rejects_exactly(t, error1, ws.getWriter().closed,
+        'closed must reject with error1'),
+      promise_rejects_exactly(t, error1, closePromise,
+        'close() must reject with error1')
+    ]);
+  });
+
+}, 'Piping from an errored readable stream to a closing writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  const closePromise = writer.close();
+  writer.releaseLock();
+
+  return flushAsyncEvents().then(() => {
+    return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the readable stream\'s error').then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return Promise.all([
+        promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+        ws.getWriter().closed,
+        closePromise
+      ]);
+    });
+  });
+
+}, 'Piping from an errored readable stream to a closed writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+  const ws = recordingWritableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the writable stream\'s error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed, 'the writable stream must be errored with error1')
+    ]);
+  });
+
+}, 'Piping from a closed readable stream to an erroring writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+  return createErroredWritableStream(t)
+  .then(ws => promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the writable stream\'s error'))
+  .then(() => {
+    assert_array_equals(rs.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Piping from a closed readable stream to an errored writable stream');
+
+promise_test(() => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return rs.pipeTo(ws).then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Piping from a closed readable stream to a closed writable stream');
diff --git a/testing/web-platform/tests/streams/piping/pipe-through.any.js b/testing/web-platform/tests/streams/piping/pipe-through.any.js
new file mode 100644
index 0000000000..26b1cd26a3
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/pipe-through.any.js
@@ -0,0 +1,331 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+function duckTypedPassThroughTransform() {
+  let enqueueInReadable;
+  let closeReadable;
+
+  return {
+    writable: new WritableStream({
+      write(chunk) {
+        enqueueInReadable(chunk);
+      },
+
+      close() {
+        closeReadable();
+      }
+    }),
+
+    readable: new ReadableStream({
+      start(c) {
+        enqueueInReadable = c.enqueue.bind(c);
+        closeReadable = c.close.bind(c);
+      }
+    })
+  };
+}
+
+function uninterestingReadableWritablePair() {
+  return { writable: new WritableStream(), readable: new ReadableStream() };
+}
+
+promise_test(() => {
+  const readableEnd = sequentialReadableStream(5).pipeThrough(duckTypedPassThroughTransform());
+
+  return readableStreamToArray(readableEnd).then(chunks =>
+    assert_array_equals(chunks, [1, 2, 3, 4, 5]), 'chunks should match');
+}, 'Piping through a duck-typed pass-through transform stream should work');
+
+promise_test(() => {
+  const transform = {
+    writable: new WritableStream({
+      start(c) {
+        c.error(new Error('this rejection should not be reported as unhandled'));
+      }
+    }),
+    readable: new ReadableStream()
+  };
+
+  sequentialReadableStream(5).pipeThrough(transform);
+
+  // The test harness should complain about unhandled rejections by then.
+  return flushAsyncEvents();
+
+}, 'Piping through a transform errored on the writable end does not cause an unhandled promise rejection');
+
+test(() => {
+  let calledPipeTo = false;
+  class BadReadableStream extends ReadableStream {
+    pipeTo() {
+      calledPipeTo = true;
+    }
+  }
+
+  const brs = new BadReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  const result = brs.pipeThrough({ readable, writable });
+
+  assert_false(calledPipeTo, 'the overridden pipeTo should not have been called');
+  assert_equals(result, readable, 'return value should be the passed readable property');
+}, 'pipeThrough should not call pipeTo on this');
+
+test(t => {
+  let calledFakePipeTo = false;
+  const realPipeTo = ReadableStream.prototype.pipeTo;
+  t.add_cleanup(() => {
+    ReadableStream.prototype.pipeTo = realPipeTo;
+  });
+  ReadableStream.prototype.pipeTo = () => {
+    calledFakePipeTo = true;
+  };
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  const result = rs.pipeThrough({ readable, writable });
+
+  assert_false(calledFakePipeTo, 'the monkey-patched pipeTo should not have been called');
+  assert_equals(result, readable, 'return value should be the passed readable property');
+
+}, 'pipeThrough should not call pipeTo on the ReadableStream prototype');
+
+const badReadables = [null, undefined, 0, NaN, true, 'ReadableStream', Object.create(ReadableStream.prototype)];
+for (const readable of badReadables) {
+  test(() => {
+    assert_throws_js(TypeError,
+                     ReadableStream.prototype.pipeThrough.bind(readable, uninterestingReadableWritablePair()),
+                     'pipeThrough should throw');
+  }, `pipeThrough should brand-check this and not allow '${readable}'`);
+
+  test(() => {
+    const rs = new ReadableStream();
+    let writableGetterCalled = false;
+    assert_throws_js(
+      TypeError,
+      () => rs.pipeThrough({
+        get writable() {
+          writableGetterCalled = true;
+          return new WritableStream();
+        },
+        readable
+      }),
+      'pipeThrough should brand-check readable'
+    );
+    assert_false(writableGetterCalled, 'writable should not have been accessed');
+  }, `pipeThrough should brand-check readable and not allow '${readable}'`);
+}
+
+const badWritables = [null, undefined, 0, NaN, true, 'WritableStream', Object.create(WritableStream.prototype)];
+for (const writable of badWritables) {
+  test(() => {
+    const rs = new ReadableStream({
+      start(c) {
+        c.close();
+      }
+    });
+    let readableGetterCalled = false;
+    assert_throws_js(TypeError, () => rs.pipeThrough({
+      get readable() {
+        readableGetterCalled = true;
+        return new ReadableStream();
+      },
+      writable
+    }),
+                  'pipeThrough should brand-check writable');
+    assert_true(readableGetterCalled, 'readable should have been accessed');
+  }, `pipeThrough should brand-check writable and not allow '${writable}'`);
+}
+
+test(t => {
+  const error = new Error();
+  error.name = 'custom';
+
+  const rs = new ReadableStream({
+    pull: t.unreached_func('pull should not be called')
+  }, { highWaterMark: 0 });
+
+  const throwingWritable = {
+    readable: rs,
+    get writable() {
+      throw error;
+    }
+  };
+  assert_throws_exactly(error,
+                        () => ReadableStream.prototype.pipeThrough.call(rs, throwingWritable, {}),
+                        'pipeThrough should rethrow the error thrown by the writable getter');
+
+  const throwingReadable = {
+    get readable() {
+      throw error;
+    },
+    writable: {}
+  };
+  assert_throws_exactly(error,
+                        () => ReadableStream.prototype.pipeThrough.call(rs, throwingReadable, {}),
+                        'pipeThrough should rethrow the error thrown by the readable getter');
+
+}, 'pipeThrough should rethrow errors from accessing readable or writable');
+
+const badSignals = [null, 0, NaN, true, 'AbortSignal', Object.create(AbortSignal.prototype)];
+for (const signal of badSignals) {
+  test(() => {
+    const rs = new ReadableStream();
+    assert_throws_js(TypeError, () => rs.pipeThrough(uninterestingReadableWritablePair(), { signal }),
+                     'pipeThrough should throw');
+  }, `invalid values of signal should throw; specifically '${signal}'`);
+}
+
+test(() => {
+  const rs = new ReadableStream();
+  const controller = new AbortController();
+  const signal = controller.signal;
+  rs.pipeThrough(uninterestingReadableWritablePair(), { signal });
+}, 'pipeThrough should accept a real AbortSignal');
+
+test(() => {
+  const rs = new ReadableStream();
+  rs.getReader();
+  assert_throws_js(TypeError, () => rs.pipeThrough(uninterestingReadableWritablePair()),
+                   'pipeThrough should throw');
+}, 'pipeThrough should throw if this is locked');
+
+test(() => {
+  const rs = new ReadableStream();
+  const writable = new WritableStream();
+  const readable = new ReadableStream();
+  writable.getWriter();
+  assert_throws_js(TypeError, () => rs.pipeThrough({writable, readable}),
+                   'pipeThrough should throw');
+}, 'pipeThrough should throw if writable is locked');
+
+test(() => {
+  const rs = new ReadableStream();
+  const writable = new WritableStream();
+  const readable = new ReadableStream();
+  readable.getReader();
+  assert_equals(rs.pipeThrough({ writable, readable }), readable,
+                'pipeThrough should not throw');
+}, 'pipeThrough should not care if readable is locked');
+
+promise_test(() => {
+  const rs = recordingReadableStream();
+  const writable = new WritableStream({
+    start(controller) {
+      controller.error();
+    }
+  });
+  const readable = new ReadableStream();
+  rs.pipeThrough({ writable, readable }, { preventCancel: true });
+  return flushAsyncEvents(0).then(() => {
+    assert_array_equals(rs.events, ['pull'], 'cancel should not have been called');
+  });
+}, 'preventCancel should work');
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const writable = recordingWritableStream();
+  const readable = new ReadableStream();
+  rs.pipeThrough({ writable, readable }, { preventClose: true });
+  return flushAsyncEvents(0).then(() => {
+    assert_array_equals(writable.events, [], 'writable should not be closed');
+  });
+}, 'preventClose should work');
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.error();
+    }
+  });
+  const writable = recordingWritableStream();
+  const readable = new ReadableStream();
+  rs.pipeThrough({ writable, readable }, { preventAbort: true });
+  return flushAsyncEvents(0).then(() => {
+    assert_array_equals(writable.events, [], 'writable should not be aborted');
+  });
+}, 'preventAbort should work');
+
+test(() => {
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  assert_throws_js(TypeError, () => rs.pipeThrough({readable, writable}, {
+    get preventAbort() {
+      writable.getWriter();
+    }
+  }), 'pipeThrough should throw');
+}, 'pipeThrough() should throw if an option getter grabs a writer');
+
+test(() => {
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  rs.pipeThrough({readable, writable}, null);
+}, 'pipeThrough() should not throw if option is null');
+
+test(() => {
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  rs.pipeThrough({readable, writable}, {signal:undefined});
+}, 'pipeThrough() should not throw if signal is undefined');
+
+function tryPipeThrough(pair, options)
+{
+  const rs = new ReadableStream();
+  if (!pair)
+    pair = {readable:new ReadableStream(), writable:new WritableStream()};
+  try {
+    rs.pipeThrough(pair, options)
+  } catch (e) {
+    return e;
+  }
+}
+
+test(() => {
+  let result = tryPipeThrough({
+    get readable() {
+      return new ReadableStream();
+    },
+    get writable() {
+      throw "writable threw";
+    }
+  }, { });
+  assert_equals(result, "writable threw");
+
+  result = tryPipeThrough({
+    get readable() {
+      throw "readable threw";
+    },
+    get writable() {
+      throw "writable threw";
+    }
+  }, { });
+  assert_equals(result, "readable threw");
+
+  result = tryPipeThrough({
+    get readable() {
+      throw "readable threw";
+    },
+    get writable() {
+      throw "writable threw";
+    }
+  }, {
+    get preventAbort() {
+      throw "preventAbort threw";
+    }
+  });
+  assert_equals(result, "readable threw");
+
+}, 'pipeThrough() should throw if readable/writable getters throw');
diff --git a/testing/web-platform/tests/streams/piping/then-interception.any.js b/testing/web-platform/tests/streams/piping/then-interception.any.js
new file mode 100644
index 0000000000..543f916d94
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/then-interception.any.js
@@ -0,0 +1,68 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+function interceptThen() {
+  const intercepted = [];
+  let callCount = 0;
+  Object.prototype.then = function(resolver) {
+    if (!this.done) {
+      intercepted.push(this.value);
+    }
+    const retval = Object.create(null);
+    retval.done = ++callCount === 3;
+    retval.value = callCount;
+    resolver(retval);
+    if (retval.done) {
+      delete Object.prototype.then;
+    }
+  }
+  return intercepted;
+}
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.close();
+    }
+  });
+  const ws = recordingWritableStream();
+
+  const intercepted = interceptThen();
+  t.add_cleanup(() => {
+    delete Object.prototype.then;
+  });
+
+  await rs.pipeTo(ws);
+  delete Object.prototype.then;
+
+
+  assert_array_equals(intercepted, [], 'nothing should have been intercepted');
+  assert_array_equals(ws.events, ['write', 'a', 'close'], 'written chunk should be "a"');
+}, 'piping should not be observable');
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.close();
+    }
+  });
+  const ws = recordingWritableStream();
+
+  const [ branch1, branch2 ] = rs.tee();
+
+  const intercepted = interceptThen();
+  t.add_cleanup(() => {
+    delete Object.prototype.then;
+  });
+
+  await branch1.pipeTo(ws);
+  delete Object.prototype.then;
+  branch2.cancel();
+
+  assert_array_equals(intercepted, [], 'nothing should have been intercepted');
+  assert_array_equals(ws.events, ['write', 'a', 'close'], 'written chunk should be "a"');
+}, 'tee should not be observable');
diff --git a/testing/web-platform/tests/streams/piping/throwing-options.any.js b/testing/web-platform/tests/streams/piping/throwing-options.any.js
new file mode 100644
index 0000000000..b9f906778f
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/throwing-options.any.js
@@ -0,0 +1,65 @@
+// META: global=window,worker
+'use strict';
+
+class ThrowingOptions {
+  constructor(whatShouldThrow) {
+    this.whatShouldThrow = whatShouldThrow;
+    this.touched = [];
+  }
+
+  get preventClose() {
+    this.maybeThrow('preventClose');
+    return false;
+  }
+
+  get preventAbort() {
+    this.maybeThrow('preventAbort');
+    return false;
+  }
+
+  get preventCancel() {
+    this.maybeThrow('preventCancel');
+    return false;
+  }
+
+  get signal() {
+    this.maybeThrow('signal');
+    return undefined;
+  }
+
+  maybeThrow(forWhat) {
+    this.touched.push(forWhat);
+    if (this.whatShouldThrow === forWhat) {
+      throw new Error(this.whatShouldThrow);
+    }
+  }
+}
+
+const checkOrder = ['preventAbort', 'preventCancel', 'preventClose', 'signal'];
+
+for (let i = 0; i < checkOrder.length; ++i) {
+  const whatShouldThrow = checkOrder[i];
+  const whatShouldBeTouched = checkOrder.slice(0, i + 1);
+
+  promise_test(t => {
+    const options = new ThrowingOptions(whatShouldThrow);
+    return promise_rejects_js(
+               t, Error,
+               new ReadableStream().pipeTo(new WritableStream(), options),
+               'pipeTo should reject')
+        .then(() => assert_array_equals(
+            options.touched, whatShouldBeTouched,
+            'options should be touched in the right order'));
+  }, `pipeTo should stop after getting ${whatShouldThrow} throws`);
+
+  test(() => {
+    const options = new ThrowingOptions(whatShouldThrow);
+    assert_throws_js(
+        Error,
+        () => new ReadableStream().pipeThrough(new TransformStream(), options),
+        'pipeThrough should throw');
+    assert_array_equals(
+        options.touched, whatShouldBeTouched,
+        'options should be touched in the right order');
+  }, `pipeThrough should stop after getting ${whatShouldThrow} throws`);
+}
diff --git a/testing/web-platform/tests/streams/piping/transform-streams.any.js b/testing/web-platform/tests/streams/piping/transform-streams.any.js
new file mode 100644
index 0000000000..caae9fbad8
--- /dev/null
+++ b/testing/web-platform/tests/streams/piping/transform-streams.any.js
@@ -0,0 +1,22 @@
+// META: global=window,worker
+'use strict';
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.enqueue('c');
+      c.close();
+    }
+  });
+
+  const ts = new TransformStream();
+
+  const ws = new WritableStream();
+
+  return rs.pipeThrough(ts).pipeTo(ws).then(() => {
+    const writer = ws.getWriter();
+    return writer.closed;
+  });
+}, 'Piping through an identity transform stream should close the destination when the source closes');
diff --git a/testing/web-platform/tests/streams/queuing-strategies-size-function-per-global.window.js b/testing/web-platform/tests/streams/queuing-strategies-size-function-per-global.window.js
new file mode 100644
index 0000000000..0f869f13b3
--- /dev/null
+++ b/testing/web-platform/tests/streams/queuing-strategies-size-function-per-global.window.js
@@ -0,0 +1,14 @@
+const iframe = document.createElement('iframe');
+document.body.appendChild(iframe);
+
+for (const type of ['CountQueuingStrategy', 'ByteLengthQueuingStrategy']) {
+  test(() => {
+    const myQs = new window[type]({ highWaterMark: 1 });
+    const yourQs = new iframe.contentWindow[type]({ highWaterMark: 1 });
+    assert_not_equals(myQs.size, yourQs.size,
+                      'size should not be the same object');
+  }, `${type} size should be different for objects in different realms`);
+}
+
+// Cleanup the document to avoid messing up the result page.
+iframe.remove();
diff --git a/testing/web-platform/tests/streams/queuing-strategies.any.js b/testing/web-platform/tests/streams/queuing-strategies.any.js
new file mode 100644
index 0000000000..fa959ebba2
--- /dev/null
+++ b/testing/web-platform/tests/streams/queuing-strategies.any.js
@@ -0,0 +1,150 @@
+// META: global=window,worker
+'use strict';
+
+const highWaterMarkConversions = new Map([
+  [-Infinity, -Infinity],
+  [-5, -5],
+  [false, 0],
+  [true, 1],
+  [NaN, NaN],
+  ['foo', NaN],
+  ['0', 0],
+  [{}, NaN],
+  [() => {}, NaN]
+]);
+
+for (const QueuingStrategy of [CountQueuingStrategy, ByteLengthQueuingStrategy]) {
+  test(() => {
+    new QueuingStrategy({ highWaterMark: 4 });
+  }, `${QueuingStrategy.name}: Can construct a with a valid high water mark`);
+
+  test(() => {
+    const highWaterMark = 1;
+    const highWaterMarkObjectGetter = {
+      get highWaterMark() { return highWaterMark; }
+    };
+    const error = new Error('wow!');
+    const highWaterMarkObjectGetterThrowing = {
+      get highWaterMark() { throw error; }
+    };
+
+    assert_throws_js(TypeError, () => new QueuingStrategy(), 'construction fails with undefined');
+    assert_throws_js(TypeError, () => new QueuingStrategy(null), 'construction fails with null');
+    assert_throws_js(TypeError, () => new QueuingStrategy(true), 'construction fails with true');
+    assert_throws_js(TypeError, () => new QueuingStrategy(5), 'construction fails with 5');
+    assert_throws_js(TypeError, () => new QueuingStrategy({}), 'construction fails with {}');
+    assert_throws_exactly(error, () => new QueuingStrategy(highWaterMarkObjectGetterThrowing),
+      'construction fails with an object with a throwing highWaterMark getter');
+
+    assert_equals((new QueuingStrategy(highWaterMarkObjectGetter)).highWaterMark, highWaterMark);
+  }, `${QueuingStrategy.name}: Constructor behaves as expected with strange arguments`);
+
+  test(() => {
+    for (const [input, output] of highWaterMarkConversions.entries()) {
+      const strategy = new QueuingStrategy({ highWaterMark: input });
+      assert_equals(strategy.highWaterMark, output, `${input} gets set correctly`);
+    }
+  }, `${QueuingStrategy.name}: highWaterMark constructor values are converted per the unrestricted double rules`);
+
+  test(() => {
+    const size1 = (new QueuingStrategy({ highWaterMark: 5 })).size;
+    const size2 = (new QueuingStrategy({ highWaterMark: 10 })).size;
+
+    assert_equals(size1, size2);
+  }, `${QueuingStrategy.name}: size is the same function across all instances`);
+
+  test(() => {
+    const size = (new QueuingStrategy({ highWaterMark: 5 })).size;
+    assert_equals(size.name, 'size');
+  }, `${QueuingStrategy.name}: size should have the right name`);
+
+  test(() => {
+    class SubClass extends QueuingStrategy {
+      size() {
+        return 2;
+      }
+
+      subClassMethod() {
+        return true;
+      }
+    }
+
+    const sc = new SubClass({ highWaterMark: 77 });
+    assert_equals(sc.constructor.name, 'SubClass', 'constructor.name should be correct');
+    assert_equals(sc.highWaterMark, 77, 'highWaterMark should come from the parent class');
+    assert_equals(sc.size(), 2, 'size() on the subclass should override the parent');
+    assert_true(sc.subClassMethod(), 'subClassMethod() should work');
+  }, `${QueuingStrategy.name}: subclassing should work correctly`);
+
+  test(() => {
+    const size = new QueuingStrategy({ highWaterMark: 5 }).size;
+    assert_false('prototype' in size);
+  }, `${QueuingStrategy.name}: size should not have a prototype property`);
+}
+
+test(() => {
+  const size = new CountQueuingStrategy({ highWaterMark: 5 }).size;
+  assert_throws_js(TypeError, () => new size());
+}, `CountQueuingStrategy: size should not be a constructor`);
+
+test(() => {
+  const size = new ByteLengthQueuingStrategy({ highWaterMark: 5 }).size;
+  assert_throws_js(TypeError, () => new size({ byteLength: 1024 }));
+}, `ByteLengthQueuingStrategy: size should not be a constructor`);
+
+test(() => {
+  const size = (new CountQueuingStrategy({ highWaterMark: 5 })).size;
+  assert_equals(size.length, 0);
+}, 'CountQueuingStrategy: size should have the right length');
+
+test(() => {
+  const size = (new ByteLengthQueuingStrategy({ highWaterMark: 5 })).size;
+  assert_equals(size.length, 1);
+}, 'ByteLengthQueuingStrategy: size should have the right length');
+
+test(() => {
+  const size = 1024;
+  const chunk = { byteLength: size };
+  const chunkGetter = {
+    get byteLength() { return size; }
+  };
+  const error = new Error('wow!');
+  const chunkGetterThrowing = {
+    get byteLength() { throw error; }
+  };
+
+  const sizeFunction = (new CountQueuingStrategy({ highWaterMark: 5 })).size;
+
+  assert_equals(sizeFunction(), 1, 'size returns 1 with undefined');
+  assert_equals(sizeFunction(null), 1, 'size returns 1 with null');
+  assert_equals(sizeFunction('potato'), 1, 'size returns 1 with non-object type');
+  assert_equals(sizeFunction({}), 1, 'size returns 1 with empty object');
+  assert_equals(sizeFunction(chunk), 1, 'size returns 1 with a chunk');
+  assert_equals(sizeFunction(chunkGetter), 1, 'size returns 1 with chunk getter');
+  assert_equals(sizeFunction(chunkGetterThrowing), 1,
+    'size returns 1 with chunk getter that throws');
+}, 'CountQueuingStrategy: size behaves as expected with strange arguments');
+
+test(() => {
+  const size = 1024;
+  const chunk = { byteLength: size };
+  const chunkGetter = {
+    get byteLength() { return size; }
+  };
+  const error = new Error('wow!');
+  const chunkGetterThrowing = {
+    get byteLength() { throw error; }
+  };
+
+  const sizeFunction = (new ByteLengthQueuingStrategy({ highWaterMark: 5 })).size;
+
+  assert_throws_js(TypeError, () => sizeFunction(), 'size fails with undefined');
+  assert_throws_js(TypeError, () => sizeFunction(null), 'size fails with null');
+  assert_equals(sizeFunction('potato'), undefined, 'size succeeds with undefined with a random non-object type');
+  assert_equals(sizeFunction({}), undefined, 'size succeeds with undefined with an object without hwm property');
+  assert_equals(sizeFunction(chunk), size, 'size succeeds with the right amount with an object with a hwm');
+  assert_equals(sizeFunction(chunkGetter), size,
+    'size succeeds with the right amount with an object with a hwm getter');
+  assert_throws_exactly(error, () => sizeFunction(chunkGetterThrowing),
+    'size fails with the error thrown by the getter');
+}, 'ByteLengthQueuingStrategy: size behaves as expected with strange arguments');
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/bad-buffers-and-views.any.js b/testing/web-platform/tests/streams/readable-byte-streams/bad-buffers-and-views.any.js
new file mode 100644
index 0000000000..3322116b19
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/bad-buffers-and-views.any.js
@@ -0,0 +1,398 @@
+// META: global=window,worker
+'use strict';
+
+promise_test(() => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.close();
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+  const view = new Uint8Array([1, 2, 3]);
+  return reader.read(view).then(({ value, done }) => {
+    // Sanity checks
+    assert_true(value instanceof Uint8Array, 'The value read must be a Uint8Array');
+    assert_not_equals(value, view, 'The value read must not be the *same* Uint8Array');
+    assert_array_equals(value, [], 'The value read must be an empty Uint8Array, since the stream is closed');
+    assert_true(done, 'done must be true, since the stream is closed');
+
+    // The important assertions
+    assert_not_equals(value.buffer, view.buffer, 'a different ArrayBuffer must underlie the value');
+    assert_equals(view.buffer.byteLength, 0, 'the original buffer must be detached');
+  });
+}, 'ReadableStream with byte source: read()ing from a closed stream still transfers the buffer');
+
+promise_test(() => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array([1, 2, 3]));
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+  const view = new Uint8Array([4, 5, 6]);
+  return reader.read(view).then(({ value, done }) => {
+    // Sanity checks
+    assert_true(value instanceof Uint8Array, 'The value read must be a Uint8Array');
+    assert_not_equals(value, view, 'The value read must not be the *same* Uint8Array');
+    assert_array_equals(value, [1, 2, 3], 'The value read must be the enqueued Uint8Array, not the original values');
+    assert_false(done, 'done must be false, since the stream is not closed');
+
+    // The important assertions
+    assert_not_equals(value.buffer, view.buffer, 'a different ArrayBuffer must underlie the value');
+    assert_equals(view.buffer.byteLength, 0, 'the original buffer must be detached');
+  });
+}, 'ReadableStream with byte source: read()ing from a stream with queued chunks still transfers the buffer');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      const view = new Uint8Array([1, 2, 3]);
+      c.enqueue(view);
+      assert_throws_js(TypeError, () => c.enqueue(view));
+    },
+    type: 'bytes'
+  });
+}, 'ReadableStream with byte source: enqueuing an already-detached buffer throws');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      const view = new Uint8Array([]);
+      assert_throws_js(TypeError, () => c.enqueue(view));
+    },
+    type: 'bytes'
+  });
+}, 'ReadableStream with byte source: enqueuing a zero-length buffer throws');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(new ArrayBuffer(10), 0, 0);
+      assert_throws_js(TypeError, () => c.enqueue(view));
+    },
+    type: 'bytes'
+  });
+}, 'ReadableStream with byte source: enqueuing a zero-length view on a non-zero-length buffer throws');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array([1, 2, 3]));
+    },
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const view = new Uint8Array([4, 5, 6]);
+  return reader.read(view).then(() => {
+    // view is now detached
+    return promise_rejects_js(t, TypeError, reader.read(view));
+  });
+}, 'ReadableStream with byte source: reading into an already-detached buffer rejects');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array([1, 2, 3]));
+    },
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const view = new Uint8Array();
+  return promise_rejects_js(t, TypeError, reader.read(view));
+}, 'ReadableStream with byte source: reading into a zero-length buffer rejects');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array([1, 2, 3]));
+    },
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const view = new Uint8Array(new ArrayBuffer(10), 0, 0);
+  return promise_rejects_js(t, TypeError, reader.read(view));
+}, 'ReadableStream with byte source: reading into a zero-length view on a non-zero-length buffer rejects');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      // Detach it by reading into it
+      reader.read(c.byobRequest.view);
+
+      assert_throws_js(TypeError, () => c.byobRequest.respond(1),
+        'respond() must throw if the corresponding view has become detached');
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respond() throws if the BYOB request\'s buffer has been detached (in the ' +
+   'readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      c.close();
+
+      // Detach it by reading into it
+      reader.read(c.byobRequest.view);
+
+      assert_throws_js(TypeError, () => c.byobRequest.respond(0),
+        'respond() must throw if the corresponding view has become detached');
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respond() throws if the BYOB request\'s buffer has been detached (in the ' +
+   'closed state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      // Detach it by reading into it
+      const view = new Uint8Array([1, 2, 3]);
+      reader.read(view);
+
+      assert_throws_js(TypeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer has been detached ' +
+    '(in the readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array();
+
+      assert_throws_js(TypeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer is zero-length ' +
+    '(in the readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array(c.byobRequest.view.buffer, 0, 0);
+
+      assert_throws_js(TypeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view is zero-length on a ' +
+    'non-zero-length buffer (in the readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = c.byobRequest.view.subarray(1, 2);
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view has a different offset ' +
+   '(in the readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      c.close();
+
+      const view = c.byobRequest.view.subarray(1, 1);
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view has a different offset ' +
+   '(in the closed state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array(new ArrayBuffer(10), 0, 3);
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer has a ' +
+   'different length (in the readable state)');
+
+async_test(t => {
+  // Tests https://github.com/nodejs/node/issues/41886
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array(new ArrayBuffer(11), 0, 3);
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes',
+    autoAllocateChunkSize: 10
+  });
+  const reader = stream.getReader();
+
+  reader.read();
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer has a ' +
+   'different length (autoAllocateChunkSize)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array(c.byobRequest.view.buffer, 0, 4);
+      view[0] = 20;
+      view[1] = 21;
+      view[2] = 22;
+      view[3] = 23;
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const buffer = new ArrayBuffer(10);
+  const view = new Uint8Array(buffer, 0, 3);
+  view[0] = 10;
+  view[1] = 11;
+  view[2] = 12;
+  reader.read(view);
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view has a larger length ' +
+   '(in the readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      c.close();
+
+      // Detach it by reading into it
+      const view = new Uint8Array([1, 2, 3]);
+      reader.read(view);
+
+      assert_throws_js(TypeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer has been detached ' +
+   '(in the closed state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array();
+
+      c.close();
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer is zero-length ' +
+   '(in the closed state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array(c.byobRequest.view.buffer, 0, 1);
+
+      c.close();
+
+      assert_throws_js(TypeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view is non-zero-length ' +
+   '(in the closed state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      const view = new Uint8Array(new ArrayBuffer(10), 0, 0);
+
+      c.close();
+
+      assert_throws_js(RangeError, () => c.byobRequest.respondWithNewView(view));
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: respondWithNewView() throws if the supplied view\'s buffer has a ' +
+   'different length (in the closed state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      // Detach it by reading into it
+      reader.read(c.byobRequest.view);
+
+      assert_throws_js(TypeError, () => c.enqueue(new Uint8Array([1])),
+        'enqueue() must throw if the BYOB request\'s buffer has become detached');
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: enqueue() throws if the BYOB request\'s buffer has been detached (in the ' +
+  'readable state)');
+
+async_test(t => {
+  const stream = new ReadableStream({
+    pull: t.step_func_done(c => {
+      c.close();
+
+      // Detach it by reading into it
+      reader.read(c.byobRequest.view);
+
+      assert_throws_js(TypeError, () => c.enqueue(new Uint8Array([1])),
+        'enqueue() must throw if the BYOB request\'s buffer has become detached');
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  reader.read(new Uint8Array([4, 5, 6]));
+}, 'ReadableStream with byte source: enqueue() throws if the BYOB request\'s buffer has been detached (in the ' +
+  'closed state)');
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/construct-byob-request.any.js b/testing/web-platform/tests/streams/readable-byte-streams/construct-byob-request.any.js
new file mode 100644
index 0000000000..8d460a1c81
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/construct-byob-request.any.js
@@ -0,0 +1,53 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+'use strict';
+
+// Prior to whatwg/stream#870 it was possible to construct a ReadableStreamBYOBRequest directly. This made it possible
+// to construct requests that were out-of-sync with the state of the ReadableStream. They could then be used to call
+// internal operations, resulting in asserts or bad behaviour. This file contains regression tests for the change.
+
+function getRealByteStreamController() {
+  let controller;
+  new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+  return controller;
+}
+
+// Create an object pretending to have prototype |prototype|, of type |type|. |type| is one of "undefined", "null",
+// "fake", or "real". "real" will call the realObjectCreator function to get a real instance of the object.
+function createDummyObject(prototype, type, realObjectCreator) {
+  switch (type) {
+    case 'undefined':
+      return undefined;
+
+    case 'null':
+      return null;
+
+    case 'fake':
+      return Object.create(prototype);
+
+    case 'real':
+      return realObjectCreator();
+  }
+
+  throw new Error('not reached');
+}
+
+const dummyTypes = ['undefined', 'null', 'fake', 'real'];
+
+for (const controllerType of dummyTypes) {
+  const controller = createDummyObject(ReadableByteStreamController.prototype, controllerType,
+                                        getRealByteStreamController);
+  for (const viewType of dummyTypes) {
+    const view = createDummyObject(Uint8Array.prototype, viewType, () => new Uint8Array(16));
+    test(() => {
+      assert_throws_js(TypeError, () => new ReadableStreamBYOBRequest(controller, view),
+                        'constructor should throw');
+    }, `ReadableStreamBYOBRequest constructor should throw when passed a ${controllerType} ` +
+        `ReadableByteStreamController and a ${viewType} view`);
+  }
+}
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/enqueue-with-detached-buffer.any.js b/testing/web-platform/tests/streams/readable-byte-streams/enqueue-with-detached-buffer.any.js
new file mode 100644
index 0000000000..d2b37f00a9
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/enqueue-with-detached-buffer.any.js
@@ -0,0 +1,21 @@
+// META: global=window,worker
+
+promise_test(async t => {
+  const error = new Error('cannot proceed');
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull: t.step_func((controller) => {
+      const buffer = controller.byobRequest.view.buffer;
+      // Detach the buffer.
+      structuredClone(buffer, { transfer: [buffer] });
+
+      // Try to enqueue with a new buffer.
+      assert_throws_js(TypeError, () => controller.enqueue(new Uint8Array([42])));
+
+      // If we got here the test passed.
+      controller.error(error);
+    })
+  });
+  const reader = rs.getReader({ mode: 'byob' });
+  await promise_rejects_exactly(t, error, reader.read(new Uint8Array(1)));
+}, 'enqueue after detaching byobRequest.view.buffer should throw');
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/general.any.js b/testing/web-platform/tests/streams/readable-byte-streams/general.any.js
new file mode 100644
index 0000000000..dd4fdc8557
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/general.any.js
@@ -0,0 +1,2901 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+test(() => {
+  assert_throws_js(TypeError, () => new ReadableStream().getReader({ mode: 'byob' }));
+}, 'getReader({mode: "byob"}) throws on non-bytes streams');
+
+
+test(() => {
+  // Constructing ReadableStream with an empty underlying byte source object as parameter shouldn't throw.
+  new ReadableStream({ type: 'bytes' }).getReader({ mode: 'byob' });
+  // Constructor must perform ToString(type).
+  new ReadableStream({ type: { toString() {return 'bytes';} } })
+    .getReader({ mode: 'byob' });
+  new ReadableStream({ type: { toString: null, valueOf() {return 'bytes';} } })
+    .getReader({ mode: 'byob' });
+}, 'ReadableStream with byte source can be constructed with no errors');
+
+test(() => {
+  const ReadableStreamBYOBReader = new ReadableStream({ type: 'bytes' }).getReader({ mode: 'byob' }).constructor;
+  const rs = new ReadableStream({ type: 'bytes' });
+
+  let reader = rs.getReader({ mode: { toString() { return 'byob'; } } });
+  assert_true(reader instanceof ReadableStreamBYOBReader, 'must give a BYOB reader');
+  reader.releaseLock();
+
+  reader = rs.getReader({ mode: { toString: null, valueOf() {return 'byob';} } });
+  assert_true(reader instanceof ReadableStreamBYOBReader, 'must give a BYOB reader');
+  reader.releaseLock();
+
+  reader = rs.getReader({ mode: 'byob', notmode: 'ignored' });
+  assert_true(reader instanceof ReadableStreamBYOBReader, 'must give a BYOB reader');
+}, 'getReader({mode}) must perform ToString()');
+
+promise_test(() => {
+  let startCalled = false;
+  let startCalledBeforePull = false;
+  let desiredSize;
+  let controller;
+
+  let resolveTestPromise;
+  const testPromise = new Promise(resolve => {
+    resolveTestPromise = resolve;
+  });
+
+  new ReadableStream({
+    start(c) {
+      controller = c;
+      startCalled = true;
+    },
+    pull() {
+      startCalledBeforePull = startCalled;
+      desiredSize = controller.desiredSize;
+      resolveTestPromise();
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 256
+  });
+
+  return testPromise.then(() => {
+    assert_true(startCalledBeforePull, 'start should be called before pull');
+    assert_equals(desiredSize, 256, 'desiredSize should equal highWaterMark');
+  });
+
+}, 'ReadableStream with byte source: Construct and expect start and pull being called');
+
+promise_test(() => {
+  let pullCount = 0;
+  let checkedNoPull = false;
+
+  let resolveTestPromise;
+  const testPromise = new Promise(resolve => {
+    resolveTestPromise = resolve;
+  });
+  let resolveStartPromise;
+
+  new ReadableStream({
+    start() {
+      return new Promise(resolve => {
+        resolveStartPromise = resolve;
+      });
+    },
+    pull() {
+      if (checkedNoPull) {
+        resolveTestPromise();
+      }
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 256
+  });
+
+  Promise.resolve().then(() => {
+    assert_equals(pullCount, 0);
+    checkedNoPull = true;
+    resolveStartPromise();
+  });
+
+  return testPromise;
+
+}, 'ReadableStream with byte source: No automatic pull call if start doesn\'t finish');
+
+test(() => {
+  assert_throws_js(Error, () => new ReadableStream({ start() { throw new Error(); }, type:'bytes' }),
+      'start() can throw an exception with type: bytes');
+}, 'ReadableStream with byte source: start() throws an exception');
+
+promise_test(t => {
+  new ReadableStream({
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  }, {
+    highWaterMark: 0
+  });
+
+  return Promise.resolve();
+}, 'ReadableStream with byte source: Construct with highWaterMark of 0');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      assert_equals(c.desiredSize, 10, 'desiredSize must start at the highWaterMark');
+      c.close();
+      assert_equals(c.desiredSize, 0, 'after closing, desiredSize must be 0');
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 10
+  });
+}, 'ReadableStream with byte source: desiredSize when closed');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      assert_equals(c.desiredSize, 10, 'desiredSize must start at the highWaterMark');
+      c.error();
+      assert_equals(c.desiredSize, null, 'after erroring, desiredSize must be null');
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 10
+  });
+}, 'ReadableStream with byte source: desiredSize when errored');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+  reader.releaseLock();
+
+  return promise_rejects_js(t, TypeError, reader.closed, 'closed must reject');
+}, 'ReadableStream with byte source: getReader(), then releaseLock()');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+  reader.releaseLock();
+
+  return promise_rejects_js(t, TypeError, reader.closed, 'closed must reject');
+}, 'ReadableStream with byte source: getReader() with mode set to byob, then releaseLock()');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.close();
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return reader.closed.then(() => {
+    assert_throws_js(TypeError, () => stream.getReader(), 'getReader() must throw');
+  });
+}, 'ReadableStream with byte source: Test that closing a stream does not release a reader automatically');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.close();
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.closed.then(() => {
+    assert_throws_js(TypeError, () => stream.getReader({ mode: 'byob' }), 'getReader() must throw');
+  });
+}, 'ReadableStream with byte source: Test that closing a stream does not release a BYOB reader automatically');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.error(error1);
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return promise_rejects_exactly(t, error1, reader.closed, 'closed must reject').then(() => {
+    assert_throws_js(TypeError, () => stream.getReader(), 'getReader() must throw');
+  });
+}, 'ReadableStream with byte source: Test that erroring a stream does not release a reader automatically');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.error(error1);
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_exactly(t, error1, reader.closed, 'closed must reject').then(() => {
+    assert_throws_js(TypeError, () => stream.getReader({ mode: 'byob' }), 'getReader() must throw');
+  });
+}, 'ReadableStream with byte source: Test that erroring a stream does not release a BYOB reader automatically');
+
+promise_test(async t => {
+  const stream = new ReadableStream({
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+  const read = reader.read();
+  reader.releaseLock();
+  await promise_rejects_js(t, TypeError, read, 'pending read must reject');
+}, 'ReadableStream with byte source: releaseLock() on ReadableStreamDefaultReader must reject pending read()');
+
+promise_test(async t => {
+  const stream = new ReadableStream({
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+  const read = reader.read(new Uint8Array(1));
+  reader.releaseLock();
+  await promise_rejects_js(t, TypeError, read, 'pending read must reject');
+}, 'ReadableStream with byte source: releaseLock() on ReadableStreamBYOBReader must reject pending read()');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  const stream = new ReadableStream({
+    pull() {
+      ++pullCount;
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 8
+  });
+
+  stream.getReader();
+
+  assert_equals(pullCount, 0, 'No pull as start() just finished and is not yet reflected to the state of the stream');
+
+  return Promise.resolve().then(() => {
+    assert_equals(pullCount, 1, 'pull must be invoked');
+  });
+}, 'ReadableStream with byte source: Automatic pull() after start()');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  const stream = new ReadableStream({
+    pull() {
+      ++pullCount;
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 0
+  });
+
+  const reader = stream.getReader();
+  reader.read();
+
+  assert_equals(pullCount, 0, 'No pull as start() just finished and is not yet reflected to the state of the stream');
+
+  return Promise.resolve().then(() => {
+    assert_equals(pullCount, 1, 'pull must be invoked');
+  });
+}, 'ReadableStream with byte source: Automatic pull() after start() and read()');
+
+// View buffers are detached after pull() returns, so record the information at the time that pull() was called.
+function extractViewInfo(view) {
+  return {
+    constructor: view.constructor,
+    bufferByteLength: view.buffer.byteLength,
+    byteOffset: view.byteOffset,
+    byteLength: view.byteLength
+  };
+}
+
+promise_test(() => {
+  let pullCount = 0;
+  let controller;
+  const byobRequests = [];
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      const byobRequest = controller.byobRequest;
+      const view = byobRequest.view;
+      byobRequests[pullCount] = {
+        nonNull: byobRequest !== null,
+        viewNonNull: view !== null,
+        viewInfo: extractViewInfo(view)
+      };
+      if (pullCount === 0) {
+        view[0] = 0x01;
+        byobRequest.respond(1);
+      } else if (pullCount === 1) {
+        view[0] = 0x02;
+        view[1] = 0x03;
+        byobRequest.respond(2);
+      }
+
+      ++pullCount;
+    },
+    type: 'bytes',
+    autoAllocateChunkSize: 16
+  }, {
+    highWaterMark: 0
+  });
+
+  const reader = stream.getReader();
+  const p0 = reader.read();
+  const p1 = reader.read();
+
+  assert_equals(pullCount, 0, 'No pull() as start() just finished and is not yet reflected to the state of the stream');
+
+  return Promise.resolve().then(() => {
+    assert_equals(pullCount, 1, 'pull() must have been invoked once');
+    const byobRequest = byobRequests[0];
+    assert_true(byobRequest.nonNull, 'first byobRequest must not be null');
+    assert_true(byobRequest.viewNonNull, 'first byobRequest.view must not be null');
+    const viewInfo = byobRequest.viewInfo;
+    assert_equals(viewInfo.constructor, Uint8Array, 'first view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 16, 'first view.buffer.byteLength should be 16');
+    assert_equals(viewInfo.byteOffset, 0, 'first view.byteOffset should be 0');
+    assert_equals(viewInfo.byteLength, 16, 'first view.byteLength should be 16');
+
+    return p0;
+  }).then(result => {
+    assert_equals(pullCount, 2, 'pull() must have been invoked twice');
+    const value = result.value;
+    assert_not_equals(value, undefined, 'first read should have a value');
+    assert_equals(value.constructor, Uint8Array, 'first value should be a Uint8Array');
+    assert_equals(value.buffer.byteLength, 16, 'first value.buffer.byteLength should be 16');
+    assert_equals(value.byteOffset, 0, 'first value.byteOffset should be 0');
+    assert_equals(value.byteLength, 1, 'first value.byteLength should be 1');
+    assert_equals(value[0], 0x01, 'first value[0] should be 0x01');
+    const byobRequest = byobRequests[1];
+    assert_true(byobRequest.nonNull, 'second byobRequest must not be null');
+    assert_true(byobRequest.viewNonNull, 'second byobRequest.view must not be null');
+    const viewInfo = byobRequest.viewInfo;
+    assert_equals(viewInfo.constructor, Uint8Array, 'second view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 16, 'second view.buffer.byteLength should be 16');
+    assert_equals(viewInfo.byteOffset, 0, 'second view.byteOffset should be 0');
+    assert_equals(viewInfo.byteLength, 16, 'second view.byteLength should be 16');
+
+    return p1;
+  }).then(result => {
+    assert_equals(pullCount, 2, 'pull() should only be invoked twice');
+    const value = result.value;
+    assert_not_equals(value, undefined, 'second read should have a value');
+    assert_equals(value.constructor, Uint8Array, 'second value should be a Uint8Array');
+    assert_equals(value.buffer.byteLength, 16, 'second value.buffer.byteLength should be 16');
+    assert_equals(value.byteOffset, 0, 'second value.byteOffset should be 0');
+    assert_equals(value.byteLength, 2, 'second value.byteLength should be 2');
+    assert_equals(value[0], 0x02, 'second value[0] should be 0x02');
+    assert_equals(value[1], 0x03, 'second value[1] should be 0x03');
+  });
+}, 'ReadableStream with byte source: autoAllocateChunkSize');
+
+promise_test(() => {
+  let pullCount = 0;
+  let controller;
+  const byobRequests = [];
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      const byobRequest = controller.byobRequest;
+      const view = byobRequest.view;
+      byobRequests[pullCount] = {
+        nonNull: byobRequest !== null,
+        viewNonNull: view !== null,
+        viewInfo: extractViewInfo(view)
+      };
+      if (pullCount === 0) {
+        view[0] = 0x01;
+        byobRequest.respond(1);
+      } else if (pullCount === 1) {
+        view[0] = 0x02;
+        view[1] = 0x03;
+        byobRequest.respond(2);
+      }
+
+      ++pullCount;
+    },
+    type: 'bytes',
+    autoAllocateChunkSize: 16
+  }, {
+    highWaterMark: 0
+  });
+
+  const reader = stream.getReader();
+  return reader.read().then(result => {
+    const value = result.value;
+    assert_not_equals(value, undefined, 'first read should have a value');
+    assert_equals(value.constructor, Uint8Array, 'first value should be a Uint8Array');
+    assert_equals(value.buffer.byteLength, 16, 'first value.buffer.byteLength should be 16');
+    assert_equals(value.byteOffset, 0, 'first value.byteOffset should be 0');
+    assert_equals(value.byteLength, 1, 'first value.byteLength should be 1');
+    assert_equals(value[0], 0x01, 'first value[0] should be 0x01');
+    const byobRequest = byobRequests[0];
+    assert_true(byobRequest.nonNull, 'first byobRequest must not be null');
+    assert_true(byobRequest.viewNonNull, 'first byobRequest.view must not be null');
+    const viewInfo = byobRequest.viewInfo;
+    assert_equals(viewInfo.constructor, Uint8Array, 'first view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 16, 'first view.buffer.byteLength should be 16');
+    assert_equals(viewInfo.byteOffset, 0, 'first view.byteOffset should be 0');
+    assert_equals(viewInfo.byteLength, 16, 'first view.byteLength should be 16');
+
+    reader.releaseLock();
+    const byobReader = stream.getReader({ mode: 'byob' });
+    return byobReader.read(new Uint8Array(32));
+  }).then(result => {
+    const value = result.value;
+    assert_not_equals(value, undefined, 'second read should have a value');
+    assert_equals(value.constructor, Uint8Array, 'second value should be a Uint8Array');
+    assert_equals(value.buffer.byteLength, 32, 'second value.buffer.byteLength should be 32');
+    assert_equals(value.byteOffset, 0, 'second value.byteOffset should be 0');
+    assert_equals(value.byteLength, 2, 'second value.byteLength should be 2');
+    assert_equals(value[0], 0x02, 'second value[0] should be 0x02');
+    assert_equals(value[1], 0x03, 'second value[1] should be 0x03');
+    const byobRequest = byobRequests[1];
+    assert_true(byobRequest.nonNull, 'second byobRequest must not be null');
+    assert_true(byobRequest.viewNonNull, 'second byobRequest.view must not be null');
+    const viewInfo = byobRequest.viewInfo;
+    assert_equals(viewInfo.constructor, Uint8Array, 'second view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 32, 'second view.buffer.byteLength should be 32');
+    assert_equals(viewInfo.byteOffset, 0, 'second view.byteOffset should be 0');
+    assert_equals(viewInfo.byteLength, 32, 'second view.byteLength should be 32');
+    assert_equals(pullCount, 2, 'pullCount should be 2');
+  });
+}, 'ReadableStream with byte source: Mix of auto allocate and BYOB');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  const stream = new ReadableStream({
+    pull() {
+      ++pullCount;
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 0
+  });
+
+  const reader = stream.getReader();
+  reader.read(new Uint8Array(8));
+
+  assert_equals(pullCount, 0, 'No pull as start() just finished and is not yet reflected to the state of the stream');
+
+  return Promise.resolve().then(() => {
+    assert_equals(pullCount, 1, 'pull must be invoked');
+  });
+}, 'ReadableStream with byte source: Automatic pull() after start() and read(view)');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  let desiredSizeInStart;
+  let desiredSizeInPull;
+
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array(16));
+      desiredSizeInStart = c.desiredSize;
+      controller = c;
+    },
+    pull() {
+      ++pullCount;
+
+      if (pullCount === 1) {
+        desiredSizeInPull = controller.desiredSize;
+      }
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 8
+  });
+
+  return Promise.resolve().then(() => {
+    assert_equals(pullCount, 0, 'No pull as the queue was filled by start()');
+    assert_equals(desiredSizeInStart, -8, 'desiredSize after enqueue() in start()');
+
+    const reader = stream.getReader();
+
+    const promise = reader.read();
+    assert_equals(pullCount, 1, 'The first pull() should be made on read()');
+    assert_equals(desiredSizeInPull, 8, 'desiredSize in pull()');
+
+    return promise.then(result => {
+      assert_false(result.done, 'result.done');
+
+      const view = result.value;
+      assert_equals(view.constructor, Uint8Array, 'view.constructor');
+      assert_equals(view.buffer.byteLength, 16, 'view.buffer');
+      assert_equals(view.byteOffset, 0, 'view.byteOffset');
+      assert_equals(view.byteLength, 16, 'view.byteLength');
+    });
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then read()');
+
+promise_test(() => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  const promise = reader.read().then(result => {
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array);
+    assert_equals(view.buffer.byteLength, 1);
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 1);
+  });
+
+  controller.enqueue(new Uint8Array(1));
+
+  return promise;
+}, 'ReadableStream with byte source: Push source that doesn\'t understand pull signal');
+
+test(() => {
+  assert_throws_js(TypeError, () => new ReadableStream({
+    pull: 'foo',
+    type: 'bytes'
+  }), 'constructor should throw');
+}, 'ReadableStream with byte source: pull() function is not callable');
+
+promise_test(() => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint16Array(16));
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return reader.read().then(result => {
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array);
+    assert_equals(view.buffer.byteLength, 32);
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 32);
+  });
+}, 'ReadableStream with byte source: enqueue() with Uint16Array, getReader(), then read()');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(16);
+      view[0] = 0x01;
+      view[8] = 0x02;
+      c.enqueue(view);
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const byobReader = stream.getReader({ mode: 'byob' });
+
+  return byobReader.read(new Uint8Array(8)).then(result => {
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array, 'value.constructor');
+    assert_equals(view.buffer.byteLength, 8, 'value.buffer.byteLength');
+    assert_equals(view.byteOffset, 0, 'value.byteOffset');
+    assert_equals(view.byteLength, 8, 'value.byteLength');
+    assert_equals(view[0], 0x01);
+
+    byobReader.releaseLock();
+
+    const reader = stream.getReader();
+
+    return reader.read();
+  }).then(result => {
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array, 'value.constructor');
+    assert_equals(view.buffer.byteLength, 16, 'value.buffer.byteLength');
+    assert_equals(view.byteOffset, 8, 'value.byteOffset');
+    assert_equals(view.byteLength, 8, 'value.byteLength');
+    assert_equals(view[0], 0x02);
+  });
+}, 'ReadableStream with byte source: enqueue(), read(view) partially, then read()');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  controller.enqueue(new Uint8Array(16));
+  controller.close();
+
+  return reader.read().then(result => {
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'byteOffset');
+    assert_equals(view.byteLength, 16, 'byteLength');
+
+    return reader.read();
+  }).then(result => {
+    assert_true(result.done, 'done');
+    assert_equals(result.value, undefined, 'value');
+  });
+}, 'ReadableStream with byte source: getReader(), enqueue(), close(), then read()');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array(16));
+      c.close();
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return reader.read().then(result => {
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'byteOffset');
+    assert_equals(view.byteLength, 16, 'byteLength');
+
+    return reader.read();
+  }).then(result => {
+    assert_true(result.done, 'done');
+    assert_equals(result.value, undefined, 'value');
+  });
+}, 'ReadableStream with byte source: enqueue(), close(), getReader(), then read()');
+
+promise_test(() => {
+  let controller;
+  let byobRequest;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      controller.enqueue(new Uint8Array(16));
+      byobRequest = controller.byobRequest;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return reader.read().then(result => {
+    assert_false(result.done, 'done');
+    assert_equals(result.value.byteLength, 16, 'byteLength');
+    assert_equals(byobRequest, null, 'byobRequest must be null');
+  });
+}, 'ReadableStream with byte source: Respond to pull() by enqueue()');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  let byobRequest;
+  const desiredSizes = [];
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequest = controller.byobRequest;
+      desiredSizes.push(controller.desiredSize);
+      controller.enqueue(new Uint8Array(1));
+      desiredSizes.push(controller.desiredSize);
+      controller.enqueue(new Uint8Array(1));
+      desiredSizes.push(controller.desiredSize);
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 0
+  });
+
+  const reader = stream.getReader();
+
+  const p0 = reader.read();
+  const p1 = reader.read();
+  const p2 = reader.read();
+
+  // Respond to the first pull call.
+  controller.enqueue(new Uint8Array(1));
+
+  assert_equals(pullCount, 0, 'pullCount after the enqueue() outside pull');
+
+  return Promise.all([p0, p1, p2]).then(result => {
+    assert_equals(pullCount, 1, 'pullCount after completion of all read()s');
+
+    assert_equals(result[0].done, false, 'result[0].done');
+    assert_equals(result[0].value.byteLength, 1, 'result[0].value.byteLength');
+    assert_equals(result[1].done, false, 'result[1].done');
+    assert_equals(result[1].value.byteLength, 1, 'result[1].value.byteLength');
+    assert_equals(result[2].done, false, 'result[2].done');
+    assert_equals(result[2].value.byteLength, 1, 'result[2].value.byteLength');
+    assert_equals(byobRequest, null, 'byobRequest should be null');
+    assert_equals(desiredSizes[0], 0, 'desiredSize on pull should be 0');
+    assert_equals(desiredSizes[1], 0, 'desiredSize after 1st enqueue() should be 0');
+    assert_equals(desiredSizes[2], 0, 'desiredSize after 2nd enqueue() should be 0');
+    assert_equals(pullCount, 1, 'pull() should only be called once');
+  });
+}, 'ReadableStream with byte source: Respond to pull() by enqueue() asynchronously');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let byobRequest;
+  const desiredSizes = [];
+
+  const stream = new ReadableStream({
+    pull(c) {
+      byobRequest = c.byobRequest;
+      desiredSizes.push(c.desiredSize);
+
+      if (pullCount < 3) {
+        c.enqueue(new Uint8Array(1));
+      } else {
+        c.close();
+      }
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  }, {
+    highWaterMark: 256
+  });
+
+  const reader = stream.getReader();
+
+  const p0 = reader.read();
+  const p1 = reader.read();
+  const p2 = reader.read();
+
+  assert_equals(pullCount, 0, 'No pull as start() just finished and is not yet reflected to the state of the stream');
+
+  return Promise.all([p0, p1, p2]).then(result => {
+    assert_equals(pullCount, 4, 'pullCount after completion of all read()s');
+
+    assert_equals(result[0].done, false, 'result[0].done');
+    assert_equals(result[0].value.byteLength, 1, 'result[0].value.byteLength');
+    assert_equals(result[1].done, false, 'result[1].done');
+    assert_equals(result[1].value.byteLength, 1, 'result[1].value.byteLength');
+    assert_equals(result[2].done, false, 'result[2].done');
+    assert_equals(result[2].value.byteLength, 1, 'result[2].value.byteLength');
+    assert_equals(byobRequest, null, 'byobRequest should be null');
+    assert_equals(desiredSizes[0], 256, 'desiredSize on pull should be 256');
+    assert_equals(desiredSizes[1], 256, 'desiredSize after 1st enqueue() should be 256');
+    assert_equals(desiredSizes[2], 256, 'desiredSize after 2nd enqueue() should be 256');
+    assert_equals(desiredSizes[3], 256, 'desiredSize after 3rd enqueue() should be 256');
+  });
+}, 'ReadableStream with byte source: Respond to multiple pull() by separate enqueue()');
+
+promise_test(() => {
+  let controller;
+
+  let pullCount = 0;
+  const byobRequestDefined = [];
+  let byobRequestViewDefined;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequestDefined.push(controller.byobRequest !== null);
+      const initialByobRequest = controller.byobRequest;
+
+      const view = controller.byobRequest.view;
+      view[0] = 0x01;
+      controller.byobRequest.respond(1);
+
+      byobRequestDefined.push(controller.byobRequest !== null);
+      byobRequestViewDefined = initialByobRequest.view !== null;
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(1)).then(result => {
+    assert_false(result.done, 'result.done');
+    assert_equals(result.value.byteLength, 1, 'result.value.byteLength');
+    assert_equals(result.value[0], 0x01, 'result.value[0]');
+    assert_equals(pullCount, 1, 'pull() should be called only once');
+    assert_true(byobRequestDefined[0], 'byobRequest must not be null before respond()');
+    assert_false(byobRequestDefined[1], 'byobRequest must be null after respond()');
+    assert_false(byobRequestViewDefined, 'view of initial byobRequest must be null after respond()');
+  });
+}, 'ReadableStream with byte source: read(view), then respond()');
+
+promise_test(() => {
+  let controller;
+
+  let pullCount = 0;
+  const byobRequestDefined = [];
+  let byobRequestViewDefined;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    async pull() {
+      byobRequestDefined.push(controller.byobRequest !== null);
+      const initialByobRequest = controller.byobRequest;
+
+      const transferredView = await transferArrayBufferView(controller.byobRequest.view);
+      transferredView[0] = 0x01;
+      controller.byobRequest.respondWithNewView(transferredView);
+
+      byobRequestDefined.push(controller.byobRequest !== null);
+      byobRequestViewDefined = initialByobRequest.view !== null;
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(1)).then(result => {
+    assert_false(result.done, 'result.done');
+    assert_equals(result.value.byteLength, 1, 'result.value.byteLength');
+    assert_equals(result.value[0], 0x01, 'result.value[0]');
+    assert_equals(pullCount, 1, 'pull() should be called only once');
+    assert_true(byobRequestDefined[0], 'byobRequest must not be null before respondWithNewView()');
+    assert_false(byobRequestDefined[1], 'byobRequest must be null after respondWithNewView()');
+    assert_false(byobRequestViewDefined, 'view of initial byobRequest must be null after respondWithNewView()');
+  });
+}, 'ReadableStream with byte source: read(view), then respondWithNewView() with a transferred ArrayBuffer');
+
+promise_test(() => {
+  let controller;
+  let byobRequestWasDefined;
+  let incorrectRespondException;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequestWasDefined = controller.byobRequest !== null;
+
+      try {
+        controller.byobRequest.respond(2);
+      } catch (e) {
+        incorrectRespondException = e;
+      }
+
+      controller.byobRequest.respond(1);
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(1)).then(() => {
+    assert_true(byobRequestWasDefined, 'byobRequest should be non-null');
+    assert_not_equals(incorrectRespondException, undefined, 'respond() must throw');
+    assert_equals(incorrectRespondException.name, 'RangeError', 'respond() must throw a RangeError');
+  });
+}, 'ReadableStream with byte source: read(view), then respond() with too big value');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  let byobRequest;
+  let viewInfo;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      ++pullCount;
+
+      byobRequest = controller.byobRequest;
+      const view = byobRequest.view;
+      viewInfo = extractViewInfo(view);
+
+      view[0] = 0x01;
+      view[1] = 0x02;
+      view[2] = 0x03;
+
+      controller.byobRequest.respond(3);
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint16Array(2)).then(result => {
+    assert_equals(pullCount, 1);
+
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'byteOffset');
+    assert_equals(view.byteLength, 2, 'byteLength');
+
+    const dataView = new DataView(view.buffer, view.byteOffset, view.byteLength);
+    assert_equals(dataView.getUint16(0), 0x0102);
+
+    return reader.read(new Uint8Array(1));
+  }).then(result => {
+    assert_equals(pullCount, 1);
+    assert_not_equals(byobRequest, null, 'byobRequest must not be null');
+    assert_equals(viewInfo.constructor, Uint8Array, 'view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 4, 'view.buffer.byteLength should be 4');
+    assert_equals(viewInfo.byteOffset, 0, 'view.byteOffset should be 0');
+    assert_equals(viewInfo.byteLength, 4, 'view.byteLength should be 4');
+
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'byteOffset');
+    assert_equals(view.byteLength, 1, 'byteLength');
+
+    assert_equals(view[0], 0x03);
+  });
+}, 'ReadableStream with byte source: respond(3) to read(view) with 2 element Uint16Array enqueues the 1 byte ' +
+   'remainder');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(controller) {
+      const view = new Uint8Array(16);
+      view[15] = 0x01;
+      controller.enqueue(view);
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(16)).then(result => {
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 16);
+    assert_equals(view[15], 0x01);
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then read(view)');
+
+promise_test(t => {
+  let cancelCount = 0;
+  let reason;
+
+  const passedReason = new TypeError('foo');
+
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array(16));
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    cancel(r) {
+      if (cancelCount === 0) {
+        reason = r;
+      }
+
+      ++cancelCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return reader.cancel(passedReason).then(result => {
+    assert_equals(result, undefined);
+    assert_equals(cancelCount, 1);
+    assert_equals(reason, passedReason, 'reason should equal the passed reason');
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then cancel() (mode = not BYOB)');
+
+promise_test(t => {
+  let cancelCount = 0;
+  let reason;
+
+  const passedReason = new TypeError('foo');
+
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array(16));
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    cancel(r) {
+      if (cancelCount === 0) {
+        reason = r;
+      }
+
+      ++cancelCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.cancel(passedReason).then(result => {
+    assert_equals(result, undefined);
+    assert_equals(cancelCount, 1);
+    assert_equals(reason, passedReason, 'reason should equal the passed reason');
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then cancel() (mode = BYOB)');
+
+promise_test(t => {
+  let cancelCount = 0;
+  let reason;
+
+  const passedReason = new TypeError('foo');
+
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    cancel(r) {
+      if (cancelCount === 0) {
+        reason = r;
+      }
+
+      ++cancelCount;
+
+      return 'bar';
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const readPromise = reader.read(new Uint8Array(1)).then(result => {
+    assert_true(result.done, 'result.done');
+    assert_equals(result.value, undefined, 'result.value');
+  });
+
+  const cancelPromise = reader.cancel(passedReason).then(result => {
+    assert_equals(result, undefined, 'cancel() return value should be fulfilled with undefined');
+    assert_equals(cancelCount, 1, 'cancel() should be called only once');
+    assert_equals(reason, passedReason, 'reason should equal the passed reason');
+  });
+
+  return Promise.all([readPromise, cancelPromise]);
+}, 'ReadableStream with byte source: getReader(), read(view), then cancel()');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  let byobRequest;
+  const viewInfos = [];
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequest = controller.byobRequest;
+
+      viewInfos.push(extractViewInfo(controller.byobRequest.view));
+      controller.enqueue(new Uint8Array(1));
+      viewInfos.push(extractViewInfo(controller.byobRequest.view));
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  return Promise.resolve().then(() => {
+    assert_equals(pullCount, 0, 'No pull() as no read(view) yet');
+
+    const reader = stream.getReader({ mode: 'byob' });
+
+    const promise = reader.read(new Uint16Array(1)).then(result => {
+      assert_true(result.done, 'result.done');
+      assert_equals(result.value, undefined, 'result.value');
+    });
+
+    assert_equals(pullCount, 1, '1 pull() should have been made in response to partial fill by enqueue()');
+    assert_not_equals(byobRequest, null, 'byobRequest should not be null');
+    assert_equals(viewInfos[0].byteLength, 2, 'byteLength before enqueue() should be 2');
+    assert_equals(viewInfos[1].byteLength, 1, 'byteLength after enqueue() should be 1');
+
+    reader.cancel();
+
+    assert_equals(pullCount, 1, 'pull() should only be called once');
+    return promise;
+  });
+}, 'ReadableStream with byte source: cancel() with partially filled pending pull() request');
+
+promise_test(() => {
+  let controller;
+  let pullCalled = false;
+
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(8);
+      view[7] = 0x01;
+      c.enqueue(view);
+
+      controller = c;
+    },
+    pull() {
+      pullCalled = true;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const buffer = new ArrayBuffer(16);
+
+  return reader.read(new Uint8Array(buffer, 8, 8)).then(result => {
+    assert_false(result.done);
+
+    assert_false(pullCalled, 'pull() must not have been called');
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array);
+    assert_equals(view.buffer.byteLength, 16);
+    assert_equals(view.byteOffset, 8);
+    assert_equals(view.byteLength, 8);
+    assert_equals(view[7], 0x01);
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then read(view) where view.buffer is not fully ' +
+   'covered by view');
+
+promise_test(() => {
+  let controller;
+  let pullCalled = false;
+
+  const stream = new ReadableStream({
+    start(c) {
+      let view;
+
+      view = new Uint8Array(16);
+      view[15] = 123;
+      c.enqueue(view);
+
+      view = new Uint8Array(8);
+      view[7] = 111;
+      c.enqueue(view);
+
+      controller = c;
+    },
+    pull() {
+      pullCalled = true;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(24)).then(result => {
+    assert_false(result.done, 'done');
+
+    assert_false(pullCalled, 'pull() must not have been called');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'byteOffset');
+    assert_equals(view.byteLength, 24, 'byteLength');
+    assert_equals(view[15], 123, 'Contents are set from the first chunk');
+    assert_equals(view[23], 111, 'Contents are set from the second chunk');
+  });
+}, 'ReadableStream with byte source: Multiple enqueue(), getReader(), then read(view)');
+
+promise_test(() => {
+  let pullCalled = false;
+
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(16);
+      view[15] = 0x01;
+      c.enqueue(view);
+    },
+    pull() {
+      pullCalled = true;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(24)).then(result => {
+    assert_false(result.done);
+
+    assert_false(pullCalled, 'pull() must not have been called');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 16);
+    assert_equals(view[15], 0x01);
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then read(view) with a bigger view');
+
+promise_test(() => {
+  let pullCalled = false;
+
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(16);
+      view[7] = 0x01;
+      view[15] = 0x02;
+      c.enqueue(view);
+    },
+    pull() {
+      pullCalled = true;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(8)).then(result => {
+    assert_false(result.done, 'done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 8);
+    assert_equals(view[7], 0x01);
+
+    return reader.read(new Uint8Array(8));
+  }).then(result => {
+    assert_false(result.done, 'done');
+
+    assert_false(pullCalled, 'pull() must not have been called');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 8);
+    assert_equals(view[7], 0x02);
+  });
+}, 'ReadableStream with byte source: enqueue(), getReader(), then read(view) with smaller views');
+
+promise_test(() => {
+  let controller;
+  let viewInfo;
+
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(1);
+      view[0] = 0xff;
+      c.enqueue(view);
+
+      controller = c;
+    },
+    pull() {
+      if (controller.byobRequest === null) {
+        return;
+      }
+
+      const view = controller.byobRequest.view;
+      viewInfo = extractViewInfo(view);
+
+      view[0] = 0xaa;
+      controller.byobRequest.respond(1);
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint16Array(1)).then(result => {
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 2);
+
+    const dataView = new DataView(view.buffer, view.byteOffset, view.byteLength);
+    assert_equals(dataView.getUint16(0), 0xffaa);
+
+    assert_equals(viewInfo.constructor, Uint8Array, 'view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 2, 'view.buffer.byteLength should be 2');
+    assert_equals(viewInfo.byteOffset, 1, 'view.byteOffset should be 1');
+    assert_equals(viewInfo.byteLength, 1, 'view.byteLength should be 1');
+  });
+}, 'ReadableStream with byte source: enqueue() 1 byte, getReader(), then read(view) with Uint16Array');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  let byobRequest;
+  let viewInfo;
+  let desiredSize;
+
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(3);
+      view[0] = 0x01;
+      view[2] = 0x02;
+      c.enqueue(view);
+
+      controller = c;
+    },
+    pull() {
+      byobRequest = controller.byobRequest;
+
+      const view = controller.byobRequest.view;
+
+      viewInfo = extractViewInfo(view);
+
+      view[0] = 0x03;
+      controller.byobRequest.respond(1);
+
+      desiredSize = controller.desiredSize;
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  // Wait for completion of the start method to be reflected.
+  return Promise.resolve().then(() => {
+    const reader = stream.getReader({ mode: 'byob' });
+
+    const promise = reader.read(new Uint16Array(2)).then(result => {
+      assert_false(result.done, 'done');
+
+      const view = result.value;
+      assert_equals(view.constructor, Uint16Array, 'constructor');
+      assert_equals(view.buffer.byteLength, 4, 'buffer.byteLength');
+      assert_equals(view.byteOffset, 0, 'byteOffset');
+      assert_equals(view.byteLength, 2, 'byteLength');
+
+      const dataView = new DataView(view.buffer, view.byteOffset, view.byteLength);
+      assert_equals(dataView.getUint16(0), 0x0100, 'contents are set');
+
+      const p = reader.read(new Uint16Array(1));
+
+      assert_equals(pullCount, 1);
+
+      return p;
+    }).then(result => {
+      assert_false(result.done, 'done');
+
+      const view = result.value;
+      assert_equals(view.buffer.byteLength, 2, 'buffer.byteLength');
+      assert_equals(view.byteOffset, 0, 'byteOffset');
+      assert_equals(view.byteLength, 2, 'byteLength');
+
+      const dataView = new DataView(view.buffer, view.byteOffset, view.byteLength);
+      assert_equals(dataView.getUint16(0), 0x0203, 'contents are set');
+
+      assert_not_equals(byobRequest, null, 'byobRequest must not be null');
+      assert_equals(viewInfo.constructor, Uint8Array, 'view.constructor should be Uint8Array');
+      assert_equals(viewInfo.bufferByteLength, 2, 'view.buffer.byteLength should be 2');
+      assert_equals(viewInfo.byteOffset, 1, 'view.byteOffset should be 1');
+      assert_equals(viewInfo.byteLength, 1, 'view.byteLength should be 1');
+      assert_equals(desiredSize, 0, 'desiredSize should be zero');
+    });
+
+    assert_equals(pullCount, 0);
+
+    return promise;
+  });
+}, 'ReadableStream with byte source: enqueue() 3 byte, getReader(), then read(view) with 2-element Uint16Array');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(1);
+      view[0] = 0xff;
+      c.enqueue(view);
+      c.close();
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+
+  return promise_rejects_js(t, TypeError, reader.read(new Uint16Array(1)), 'read(view) must fail')
+      .then(() => promise_rejects_js(t, TypeError, reader.closed, 'reader.closed should reject'));
+}, 'ReadableStream with byte source: read(view) with Uint16Array on close()-d stream with 1 byte enqueue()-d must ' +
+   'fail');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      const view = new Uint8Array(1);
+      view[0] = 0xff;
+      c.enqueue(view);
+
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const readPromise = reader.read(new Uint16Array(1));
+
+  assert_throws_js(TypeError, () => controller.close(), 'controller.close() must throw');
+
+  return promise_rejects_js(t, TypeError, readPromise, 'read(view) must fail')
+      .then(() => promise_rejects_js(t, TypeError, reader.closed, 'reader.closed must reject'));
+}, 'ReadableStream with byte source: A stream must be errored if close()-d before fulfilling read(view) with ' +
+   'Uint16Array');
+
+test(() => {
+  let controller;
+
+  new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+
+  // Enqueue a chunk so that the stream doesn't get closed. This is to check duplicate close() calls are rejected
+  // even if the stream has not yet entered the closed state.
+  const view = new Uint8Array(1);
+  controller.enqueue(view);
+  controller.close();
+
+  assert_throws_js(TypeError, () => controller.close(), 'controller.close() must throw');
+}, 'ReadableStream with byte source: Throw if close()-ed more than once');
+
+test(() => {
+  let controller;
+
+  new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+
+  // Enqueue a chunk so that the stream doesn't get closed. This is to check enqueue() after close() is  rejected
+  // even if the stream has not yet entered the closed state.
+  const view = new Uint8Array(1);
+  controller.enqueue(view);
+  controller.close();
+
+  assert_throws_js(TypeError, () => controller.enqueue(view), 'controller.close() must throw');
+}, 'ReadableStream with byte source: Throw on enqueue() after close()');
+
+promise_test(() => {
+  let controller;
+  let byobRequest;
+  let viewInfo;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequest = controller.byobRequest;
+      const view = controller.byobRequest.view;
+      viewInfo = extractViewInfo(view);
+
+      view[15] = 0x01;
+      controller.byobRequest.respond(16);
+      controller.close();
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint8Array(16)).then(result => {
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 16);
+    assert_equals(view[15], 0x01);
+
+    return reader.read(new Uint8Array(16));
+  }).then(result => {
+    assert_true(result.done);
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 0);
+
+    assert_not_equals(byobRequest, null, 'byobRequest must not be null');
+    assert_equals(viewInfo.constructor, Uint8Array, 'view.constructor should be Uint8Array');
+    assert_equals(viewInfo.bufferByteLength, 16, 'view.buffer.byteLength should be 16');
+    assert_equals(viewInfo.byteOffset, 0, 'view.byteOffset should be 0');
+    assert_equals(viewInfo.byteLength, 16, 'view.byteLength should be 16');
+  });
+}, 'ReadableStream with byte source: read(view), then respond() and close() in pull()');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  const viewInfos = [];
+  const viewInfosAfterRespond = [];
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      if (controller.byobRequest === null) {
+        return;
+      }
+
+      for (let i = 0; i < 4; ++i) {
+        const view = controller.byobRequest.view;
+        viewInfos.push(extractViewInfo(view));
+
+        view[0] = 0x01;
+        controller.byobRequest.respond(1);
+        viewInfosAfterRespond.push(extractViewInfo(view));
+      }
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint32Array(1)).then(result => {
+    assert_false(result.done, 'result.done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+    assert_equals(view.byteLength, 4, 'result.value.byteLength');
+    assert_equals(view[0], 0x01010101, 'result.value[0]');
+
+    assert_equals(pullCount, 1, 'pull() should only be called once');
+
+    for (let i = 0; i < 4; ++i) {
+      assert_equals(viewInfos[i].constructor, Uint8Array, 'view.constructor should be Uint8Array');
+      assert_equals(viewInfos[i].bufferByteLength, 4, 'view.buffer.byteLength should be 4');
+
+      assert_equals(viewInfos[i].byteOffset, i, 'view.byteOffset should be i');
+      assert_equals(viewInfos[i].byteLength, 4 - i, 'view.byteLength should be 4 - i');
+
+      assert_equals(viewInfosAfterRespond[i].bufferByteLength, 0, 'view.buffer should be transferred after respond()');
+    }
+  });
+}, 'ReadableStream with byte source: read(view) with Uint32Array, then fill it by multiple respond() calls');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  const viewInfos = [];
+  const viewInfosAfterEnqueue = [];
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      if (controller.byobRequest === null) {
+        return;
+      }
+
+      for (let i = 0; i < 4; ++i) {
+        const view = controller.byobRequest.view;
+        viewInfos.push(extractViewInfo(view));
+
+        controller.enqueue(new Uint8Array([0x01]));
+        viewInfosAfterEnqueue.push(extractViewInfo(view));
+      }
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return reader.read(new Uint32Array(1)).then(result => {
+    assert_false(result.done, 'result.done');
+
+    const view = result.value;
+    assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+    assert_equals(view.byteLength, 4, 'result.value.byteLength');
+    assert_equals(view[0], 0x01010101, 'result.value[0]');
+
+    assert_equals(pullCount, 1, 'pull() should only be called once');
+
+    for (let i = 0; i < 4; ++i) {
+      assert_equals(viewInfos[i].constructor, Uint8Array, 'view.constructor should be Uint8Array');
+      assert_equals(viewInfos[i].bufferByteLength, 4, 'view.buffer.byteLength should be 4');
+
+      assert_equals(viewInfos[i].byteOffset, i, 'view.byteOffset should be i');
+      assert_equals(viewInfos[i].byteLength, 4 - i, 'view.byteLength should be 4 - i');
+
+      assert_equals(viewInfosAfterEnqueue[i].bufferByteLength, 0, 'view.buffer should be transferred after enqueue()');
+    }
+  });
+}, 'ReadableStream with byte source: read(view) with Uint32Array, then fill it by multiple enqueue() calls');
+
+promise_test(() => {
+  let pullCount = 0;
+
+  let controller;
+  let byobRequest;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequest = controller.byobRequest;
+
+      ++pullCount;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  const p0 = reader.read().then(result => {
+    assert_equals(pullCount, 1);
+
+    controller.enqueue(new Uint8Array(2));
+
+    // Since the queue has data no less than HWM, no more pull.
+    assert_equals(pullCount, 1);
+
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array);
+    assert_equals(view.buffer.byteLength, 1);
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 1);
+  });
+
+  assert_equals(pullCount, 0, 'No pull should have been made since the startPromise has not yet been handled');
+
+  const p1 = reader.read().then(result => {
+    assert_equals(pullCount, 1);
+
+    assert_false(result.done);
+
+    const view = result.value;
+    assert_equals(view.constructor, Uint8Array);
+    assert_equals(view.buffer.byteLength, 2);
+    assert_equals(view.byteOffset, 0);
+    assert_equals(view.byteLength, 2);
+
+    assert_equals(byobRequest, null, 'byobRequest must be null');
+  });
+
+  assert_equals(pullCount, 0, 'No pull should have been made since the startPromise has not yet been handled');
+
+  controller.enqueue(new Uint8Array(1));
+
+  assert_equals(pullCount, 0, 'No pull should have been made since the startPromise has not yet been handled');
+
+  return Promise.all([p0, p1]);
+}, 'ReadableStream with byte source: read() twice, then enqueue() twice');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const p0 = reader.read(new Uint8Array(16)).then(result => {
+    assert_true(result.done, '1st read: done');
+
+    const view = result.value;
+    assert_equals(view.buffer.byteLength, 16, '1st read: buffer.byteLength');
+    assert_equals(view.byteOffset, 0, '1st read: byteOffset');
+    assert_equals(view.byteLength, 0, '1st read: byteLength');
+  });
+
+  const p1 = reader.read(new Uint8Array(32)).then(result => {
+    assert_true(result.done, '2nd read: done');
+
+    const view = result.value;
+    assert_equals(view.buffer.byteLength, 32, '2nd read: buffer.byteLength');
+    assert_equals(view.byteOffset, 0, '2nd read: byteOffset');
+    assert_equals(view.byteLength, 0, '2nd read: byteLength');
+  });
+
+  controller.close();
+  controller.byobRequest.respond(0);
+
+  return Promise.all([p0, p1]);
+}, 'ReadableStream with byte source: Multiple read(view), close() and respond()');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const p0 = reader.read(new Uint8Array(16)).then(result => {
+    assert_false(result.done, '1st read: done');
+
+    const view = result.value;
+    assert_equals(view.buffer.byteLength, 16, '1st read: buffer.byteLength');
+    assert_equals(view.byteOffset, 0, '1st read: byteOffset');
+    assert_equals(view.byteLength, 16, '1st read: byteLength');
+  });
+
+  const p1 = reader.read(new Uint8Array(16)).then(result => {
+    assert_false(result.done, '2nd read: done');
+
+    const view = result.value;
+    assert_equals(view.buffer.byteLength, 16, '2nd read: buffer.byteLength');
+    assert_equals(view.byteOffset, 0, '2nd read: byteOffset');
+    assert_equals(view.byteLength, 8, '2nd read: byteLength');
+  });
+
+  controller.enqueue(new Uint8Array(24));
+
+  return Promise.all([p0, p1]);
+}, 'ReadableStream with byte source: Multiple read(view), big enqueue()');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  let bytesRead = 0;
+
+  function pump() {
+    return reader.read(new Uint8Array(7)).then(result => {
+      if (result.done) {
+        assert_equals(bytesRead, 1024);
+        return undefined;
+      }
+
+      bytesRead += result.value.byteLength;
+
+      return pump();
+    });
+  }
+  const promise = pump();
+
+  controller.enqueue(new Uint8Array(512));
+  controller.enqueue(new Uint8Array(512));
+  controller.close();
+
+  return promise;
+}, 'ReadableStream with byte source: Multiple read(view) and multiple enqueue()');
+
+promise_test(t => {
+  let pullCalled = false;
+  const stream = new ReadableStream({
+    pull(controller) {
+      pullCalled = true;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_js(t, TypeError, reader.read(), 'read() must fail')
+      .then(() => assert_false(pullCalled, 'pull() must not have been called'));
+}, 'ReadableStream with byte source: read(view) with passing undefined as view must fail');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_js(t, TypeError, reader.read({}), 'read(view) must fail');
+}, 'ReadableStream with byte source: read(view) with passing an empty object as view must fail');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_js(t, TypeError,
+                         reader.read({ buffer: new ArrayBuffer(10), byteOffset: 0, byteLength: 10 }),
+                         'read(view) must fail');
+}, 'ReadableStream with byte source: Even read(view) with passing ArrayBufferView like object as view must fail');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.error(error1);
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return promise_rejects_exactly(t, error1, reader.read(), 'read() must fail');
+}, 'ReadableStream with byte source: read() on an errored stream');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  const promise = promise_rejects_exactly(t, error1, reader.read(), 'read() must fail');
+
+  controller.error(error1);
+
+  return promise;
+}, 'ReadableStream with byte source: read(), then error()');
+
+promise_test(t => {
+  const stream = new ReadableStream({
+    start(c) {
+      c.error(error1);
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_exactly(t, error1, reader.read(new Uint8Array(1)), 'read() must fail');
+}, 'ReadableStream with byte source: read(view) on an errored stream');
+
+promise_test(t => {
+  let controller;
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const promise = promise_rejects_exactly(t, error1, reader.read(new Uint8Array(1)), 'read() must fail');
+
+  controller.error(error1);
+
+  return promise;
+}, 'ReadableStream with byte source: read(view), then error()');
+
+promise_test(t => {
+  let controller;
+  let byobRequest;
+
+  const testError = new TypeError('foo');
+
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      byobRequest = controller.byobRequest;
+      throw testError;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  const promise = promise_rejects_exactly(t, testError, reader.read(), 'read() must fail');
+  return promise_rejects_exactly(t, testError, promise.then(() => reader.closed))
+      .then(() => assert_equals(byobRequest, null, 'byobRequest must be null'));
+}, 'ReadableStream with byte source: Throwing in pull function must error the stream');
+
+promise_test(t => {
+  let byobRequest;
+
+  const stream = new ReadableStream({
+    pull(controller) {
+      byobRequest = controller.byobRequest;
+      controller.error(error1);
+      throw new TypeError('foo');
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader();
+
+  return promise_rejects_exactly(t, error1, reader.read(), 'read() must fail')
+      .then(() => promise_rejects_exactly(t, error1, reader.closed, 'closed must fail'))
+      .then(() => assert_equals(byobRequest, null, 'byobRequest must be null'));
+}, 'ReadableStream with byte source: Throwing in pull in response to read() must be ignored if the stream is ' +
+   'errored in it');
+
+promise_test(t => {
+  let byobRequest;
+
+  const testError = new TypeError('foo');
+
+  const stream = new ReadableStream({
+    pull(controller) {
+      byobRequest = controller.byobRequest;
+      throw testError;
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_exactly(t, testError, reader.read(new Uint8Array(1)), 'read(view) must fail')
+      .then(() => promise_rejects_exactly(t, testError, reader.closed, 'reader.closed must reject'))
+      .then(() => assert_not_equals(byobRequest, null, 'byobRequest must not be null'));
+}, 'ReadableStream with byte source: Throwing in pull in response to read(view) function must error the stream');
+
+promise_test(t => {
+  let byobRequest;
+
+  const stream = new ReadableStream({
+    pull(controller) {
+      byobRequest = controller.byobRequest;
+      controller.error(error1);
+      throw new TypeError('foo');
+    },
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+
+  return promise_rejects_exactly(t, error1, reader.read(new Uint8Array(1)), 'read(view) must fail')
+      .then(() => promise_rejects_exactly(t, error1, reader.closed, 'closed must fail'))
+      .then(() => assert_not_equals(byobRequest, null, 'byobRequest must not be null'));
+}, 'ReadableStream with byte source: Throwing in pull in response to read(view) must be ignored if the stream is ' +
+   'errored in it');
+
+promise_test(() => {
+  let byobRequest;
+  const rs = new ReadableStream({
+    pull(controller) {
+      byobRequest = controller.byobRequest;
+      byobRequest.respond(4);
+    },
+    type: 'bytes'
+  });
+  const reader = rs.getReader({ mode: 'byob' });
+  const view = new Uint8Array(16);
+  return reader.read(view).then(() => {
+    assert_throws_js(TypeError, () => byobRequest.respond(4), 'respond() should throw a TypeError');
+  });
+}, 'calling respond() twice on the same byobRequest should throw');
+
+promise_test(() => {
+  let byobRequest;
+  const newView = () => new Uint8Array(16);
+  const rs = new ReadableStream({
+    pull(controller) {
+      byobRequest = controller.byobRequest;
+      byobRequest.respondWithNewView(newView());
+    },
+    type: 'bytes'
+  });
+  const reader = rs.getReader({ mode: 'byob' });
+  return reader.read(newView()).then(() => {
+    assert_throws_js(TypeError, () => byobRequest.respondWithNewView(newView()),
+                     'respondWithNewView() should throw a TypeError');
+  });
+}, 'calling respondWithNewView() twice on the same byobRequest should throw');
+
+promise_test(() => {
+  let controller;
+  let byobRequest;
+  let resolvePullCalledPromise;
+  const pullCalledPromise = new Promise(resolve => {
+    resolvePullCalledPromise = resolve;
+  });
+  let resolvePull;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull(c) {
+      byobRequest = c.byobRequest;
+      resolvePullCalledPromise();
+      return new Promise(resolve => {
+        resolvePull = resolve;
+      });
+    },
+    type: 'bytes'
+  });
+  const reader = rs.getReader({ mode: 'byob' });
+  const readPromise = reader.read(new Uint8Array(16));
+  return pullCalledPromise.then(() => {
+    controller.close();
+    byobRequest.respond(0);
+    resolvePull();
+    return readPromise.then(() => {
+      assert_throws_js(TypeError, () => byobRequest.respond(0), 'respond() should throw');
+    });
+  });
+}, 'calling respond(0) twice on the same byobRequest should throw even when closed');
+
+promise_test(() => {
+  let controller;
+  let byobRequest;
+  let resolvePullCalledPromise;
+  const pullCalledPromise = new Promise(resolve => {
+    resolvePullCalledPromise = resolve;
+  });
+  let resolvePull;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull(c) {
+      byobRequest = c.byobRequest;
+      resolvePullCalledPromise();
+      return new Promise(resolve => {
+        resolvePull = resolve;
+      });
+    },
+    type: 'bytes'
+  });
+  const reader = rs.getReader({ mode: 'byob' });
+  const readPromise = reader.read(new Uint8Array(16));
+  return pullCalledPromise.then(() => {
+    const cancelPromise = reader.cancel('meh');
+    assert_throws_js(TypeError, () => byobRequest.respond(0), 'respond() should throw');
+    resolvePull();
+    return Promise.all([readPromise, cancelPromise]);
+  });
+}, 'calling respond() should throw when canceled');
+
+promise_test(async t => {
+  let resolvePullCalledPromise;
+  const pullCalledPromise = new Promise(resolve => {
+    resolvePullCalledPromise = resolve;
+  });
+  let resolvePull;
+  const rs = new ReadableStream({
+    pull() {
+      resolvePullCalledPromise();
+      return new Promise(resolve => {
+        resolvePull = resolve;
+      });
+    },
+    type: 'bytes'
+  });
+  const reader = rs.getReader({ mode: 'byob' });
+  const read = reader.read(new Uint8Array(16));
+  await pullCalledPromise;
+  resolvePull();
+  await delay(0);
+  reader.releaseLock();
+  await promise_rejects_js(t, TypeError, read, 'pending read should reject');
+}, 'pull() resolving should not resolve read()');
+
+promise_test(() => {
+  // Tests https://github.com/whatwg/streams/issues/686
+
+  let controller;
+  const rs = new ReadableStream({
+    autoAllocateChunkSize: 128,
+    start(c) {
+      controller = c;
+    },
+    type: 'bytes'
+  });
+
+  const readPromise = rs.getReader().read();
+
+  const br = controller.byobRequest;
+  controller.close();
+
+  br.respond(0);
+
+  return readPromise;
+}, 'ReadableStream with byte source: default reader + autoAllocateChunkSize + byobRequest interaction');
+
+test(() => {
+  assert_throws_js(TypeError, () => new ReadableStream({ autoAllocateChunkSize: 0, type: 'bytes' }),
+      'controller cannot be setup with autoAllocateChunkSize = 0');
+}, 'ReadableStream with byte source: autoAllocateChunkSize cannot be 0');
+
+test(() => {
+  const ReadableStreamBYOBReader = new ReadableStream({ type: 'bytes' }).getReader({ mode: 'byob' }).constructor;
+  const stream = new ReadableStream({ type: 'bytes' });
+  new ReadableStreamBYOBReader(stream);
+}, 'ReadableStreamBYOBReader can be constructed directly');
+
+test(() => {
+  const ReadableStreamBYOBReader = new ReadableStream({ type: 'bytes' }).getReader({ mode: 'byob' }).constructor;
+  assert_throws_js(TypeError, () => new ReadableStreamBYOBReader({}), 'constructor must throw');
+}, 'ReadableStreamBYOBReader constructor requires a ReadableStream argument');
+
+test(() => {
+  const ReadableStreamBYOBReader = new ReadableStream({ type: 'bytes' }).getReader({ mode: 'byob' }).constructor;
+  const stream = new ReadableStream({ type: 'bytes' });
+  stream.getReader();
+  assert_throws_js(TypeError, () => new ReadableStreamBYOBReader(stream), 'constructor must throw');
+}, 'ReadableStreamBYOBReader constructor requires an unlocked ReadableStream');
+
+test(() => {
+  const ReadableStreamBYOBReader = new ReadableStream({ type: 'bytes' }).getReader({ mode: 'byob' }).constructor;
+  const stream = new ReadableStream();
+  assert_throws_js(TypeError, () => new ReadableStreamBYOBReader(stream), 'constructor must throw');
+}, 'ReadableStreamBYOBReader constructor requires a ReadableStream with type "bytes"');
+
+test(() => {
+  assert_throws_js(RangeError, () => new ReadableStream({ type: 'bytes' }, {
+    size() {
+      return 1;
+    }
+  }), 'constructor should throw for size function');
+
+  assert_throws_js(RangeError,
+                   () => new ReadableStream({ type: 'bytes' }, new CountQueuingStrategy({ highWaterMark: 1 })),
+                   'constructor should throw when strategy is CountQueuingStrategy');
+
+  assert_throws_js(RangeError,
+                   () => new ReadableStream({ type: 'bytes' }, new ByteLengthQueuingStrategy({ highWaterMark: 512 })),
+                   'constructor should throw when strategy is ByteLengthQueuingStrategy');
+
+  class HasSizeMethod {
+    size() {}
+ }
+
+  assert_throws_js(RangeError, () => new ReadableStream({ type: 'bytes' }, new HasSizeMethod()),
+                   'constructor should throw when size on the prototype chain');
+}, 'ReadableStream constructor should not accept a strategy with a size defined if type is "bytes"');
+
+promise_test(async t => {
+  const stream = new ReadableStream({
+    pull: t.step_func(c => {
+      const view = new Uint8Array(c.byobRequest.view.buffer, 0, 1);
+      view[0] = 1;
+
+      c.byobRequest.respondWithNewView(view);
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const result = await reader.read(new Uint8Array([4, 5, 6]));
+  assert_false(result.done, 'result.done');
+
+  const view = result.value;
+  assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+  assert_equals(view.byteLength, 1, 'result.value.byteLength');
+  assert_equals(view[0], 1, 'result.value[0]');
+  assert_equals(view.buffer.byteLength, 3, 'result.value.buffer.byteLength');
+  assert_array_equals([...new Uint8Array(view.buffer)], [1, 5, 6], 'result.value.buffer');
+}, 'ReadableStream with byte source: respondWithNewView() with a smaller view');
+
+promise_test(async t => {
+  const stream = new ReadableStream({
+    pull: t.step_func(c => {
+      const view = new Uint8Array(c.byobRequest.view.buffer, 0, 0);
+
+      c.close();
+
+      c.byobRequest.respondWithNewView(view);
+    }),
+    type: 'bytes'
+  });
+  const reader = stream.getReader({ mode: 'byob' });
+
+  const result = await reader.read(new Uint8Array([4, 5, 6]));
+  assert_true(result.done, 'result.done');
+
+  const view = result.value;
+  assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+  assert_equals(view.byteLength, 0, 'result.value.byteLength');
+  assert_equals(view.buffer.byteLength, 3, 'result.value.buffer.byteLength');
+  assert_array_equals([...new Uint8Array(view.buffer)], [4, 5, 6], 'result.value.buffer');
+}, 'ReadableStream with byte source: respondWithNewView() with a zero-length view (in the closed state)');
+
+promise_test(async t => {
+  let controller;
+  let resolvePullCalledPromise;
+  const pullCalledPromise = new Promise(resolve => {
+    resolvePullCalledPromise = resolve;
+  });
+  const stream = new ReadableStream({
+    start: t.step_func((c) => {
+      controller = c;
+    }),
+    pull: t.step_func(() => {
+      resolvePullCalledPromise();
+    }),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+  const readPromise = reader.read(new Uint8Array([4, 5, 6]));
+  await pullCalledPromise;
+
+  // Transfer the original BYOB request's buffer, and respond with a new view on that buffer
+  const transferredView = await transferArrayBufferView(controller.byobRequest.view);
+  const newView = transferredView.subarray(0, 1);
+  newView[0] = 42;
+
+  controller.byobRequest.respondWithNewView(newView);
+
+  const result = await readPromise;
+  assert_false(result.done, 'result.done');
+
+  const view = result.value;
+  assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+  assert_equals(view.byteLength, 1, 'result.value.byteLength');
+  assert_equals(view[0], 42, 'result.value[0]');
+  assert_equals(view.buffer.byteLength, 3, 'result.value.buffer.byteLength');
+  assert_array_equals([...new Uint8Array(view.buffer)], [42, 5, 6], 'result.value.buffer');
+
+}, 'ReadableStream with byte source: respondWithNewView() with a transferred non-zero-length view ' +
+   '(in the readable state)');
+
+promise_test(async t => {
+  let controller;
+  let resolvePullCalledPromise;
+  const pullCalledPromise = new Promise(resolve => {
+    resolvePullCalledPromise = resolve;
+  });
+  const stream = new ReadableStream({
+    start: t.step_func((c) => {
+      controller = c;
+    }),
+    pull: t.step_func(() => {
+      resolvePullCalledPromise();
+    }),
+    type: 'bytes'
+  });
+
+  const reader = stream.getReader({ mode: 'byob' });
+  const readPromise = reader.read(new Uint8Array([4, 5, 6]));
+  await pullCalledPromise;
+
+  // Transfer the original BYOB request's buffer, and respond with an empty view on that buffer
+  const transferredView = await transferArrayBufferView(controller.byobRequest.view);
+  const newView = transferredView.subarray(0, 0);
+
+  controller.close();
+  controller.byobRequest.respondWithNewView(newView);
+
+  const result = await readPromise;
+  assert_true(result.done, 'result.done');
+
+  const view = result.value;
+  assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+  assert_equals(view.byteLength, 0, 'result.value.byteLength');
+  assert_equals(view.buffer.byteLength, 3, 'result.value.buffer.byteLength');
+  assert_array_equals([...new Uint8Array(view.buffer)], [4, 5, 6], 'result.value.buffer');
+
+}, 'ReadableStream with byte source: respondWithNewView() with a transferred zero-length view ' +
+   '(in the closed state)');
+
+promise_test(async t => {
+  let controller;
+  let pullCount = 0;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 10,
+    start: t.step_func((c) => {
+      controller = c;
+    }),
+    pull: t.step_func(() => {
+      ++pullCount;
+    })
+  });
+
+  await flushAsyncEvents();
+  assert_equals(pullCount, 0, 'pull() must not have been invoked yet');
+
+  const reader1 = rs.getReader();
+  const read1 = reader1.read();
+  assert_equals(pullCount, 1, 'pull() must have been invoked once');
+  const byobRequest1 = controller.byobRequest;
+  assert_equals(byobRequest1.view.byteLength, 10, 'first byobRequest.view.byteLength');
+
+  // enqueue() must discard the auto-allocated BYOB request
+  controller.enqueue(new Uint8Array([1, 2, 3]));
+  assert_equals(byobRequest1.view, null, 'first byobRequest must be invalidated after enqueue()');
+
+  const result1 = await read1;
+  assert_false(result1.done, 'first result.done');
+  const view1 = result1.value;
+  assert_equals(view1.byteOffset, 0, 'first result.value.byteOffset');
+  assert_equals(view1.byteLength, 3, 'first result.value.byteLength');
+  assert_array_equals([...new Uint8Array(view1.buffer)], [1, 2, 3], 'first result.value.buffer');
+
+  reader1.releaseLock();
+
+  // read(view) should work after discarding the auto-allocated BYOB request
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_equals(pullCount, 2, 'pull() must have been invoked twice');
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2.view.byteOffset, 0, 'second byobRequest.view.byteOffset');
+  assert_equals(byobRequest2.view.byteLength, 3, 'second byobRequest.view.byteLength');
+  assert_array_equals([...new Uint8Array(byobRequest2.view.buffer)], [4, 5, 6], 'second byobRequest.view.buffer');
+
+  byobRequest2.respond(3);
+  assert_equals(byobRequest2.view, null, 'second byobRequest must be invalidated after respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  const view2 = result2.value;
+  assert_equals(view2.byteOffset, 0, 'second result.value.byteOffset');
+  assert_equals(view2.byteLength, 3, 'second result.value.byteLength');
+  assert_array_equals([...new Uint8Array(view2.buffer)], [4, 5, 6], 'second result.value.buffer');
+
+  reader2.releaseLock();
+  assert_equals(pullCount, 2, 'pull() must only have been invoked twice');
+}, 'ReadableStream with byte source: enqueue() discards auto-allocated BYOB request');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint8Array([1, 2, 3]));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([1, 2, 3]), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  assert_equals(controller.byobRequest, byobRequest1, 'byobRequest should be unchanged');
+  assert_array_equals([...new Uint8Array(byobRequest1.view.buffer)], [1, 2, 3], 'byobRequest.view.buffer should be unchanged');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // respond() should fulfill the *second* read() request
+  byobRequest1.view[0] = 11;
+  byobRequest1.respond(1);
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11, 5, 6]).subarray(0, 1), 'second result.value');
+
+}, 'ReadableStream with byte source: releaseLock() with pending read(view), read(view) on second reader, respond()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint8Array([1, 2, 3]));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([1, 2, 3]), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint16Array(1));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  assert_equals(controller.byobRequest, byobRequest1, 'byobRequest should be unchanged');
+  assert_array_equals([...new Uint8Array(byobRequest1.view.buffer)], [1, 2, 3], 'byobRequest.view.buffer should be unchanged');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // respond(1) should partially fill the second read(), but not yet fulfill it
+  byobRequest1.view[0] = 0x11;
+  byobRequest1.respond(1);
+
+  // second BYOB request should use remaining buffer from the second read()
+  const byobRequest2 = controller.byobRequest;
+  assert_not_equals(byobRequest2, null, 'second byobRequest should exist');
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11, 0]).subarray(1, 2), 'second byobRequest.view');
+
+  // second respond(1) should fill the read request and fulfill it
+  byobRequest2.view[0] = 0x22;
+  byobRequest2.respond(1);
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  const view2 = result2.value;
+  assert_equals(view2.byteOffset, 0, 'second result.value.byteOffset');
+  assert_equals(view2.byteLength, 2, 'second result.value.byteLength');
+  const dataView2 = new DataView(view2.buffer, view2.byteOffset, view2.byteLength);
+  assert_equals(dataView2.getUint16(0), 0x1122, 'second result.value[0]');
+
+}, 'ReadableStream with byte source: releaseLock() with pending read(view), read(view) on second reader with ' +
+   '1 element Uint16Array, respond(1)');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint8Array([1, 2, 3]));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([1, 2, 3]), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  assert_equals(controller.byobRequest, byobRequest1, 'byobRequest should be unchanged');
+  assert_array_equals([...new Uint8Array(byobRequest1.view.buffer)], [1, 2, 3], 'byobRequest.view.buffer should be unchanged');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // respond(3) should fulfill the second read(), and put 1 remaining byte in the queue
+  byobRequest1.view[0] = 6;
+  byobRequest1.view[1] = 7;
+  byobRequest1.view[2] = 8;
+  byobRequest1.respond(3);
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([6, 7]), 'second result.value');
+
+  // third read() should fulfill with the remaining byte
+  const result3 = await reader2.read(new Uint8Array([0, 0, 0]));
+  assert_false(result3.done, 'third result.done');
+  assert_typed_array_equals(result3.value, new Uint8Array([8, 0, 0]).subarray(0, 1), 'third result.value');
+
+}, 'ReadableStream with byte source: releaseLock() with pending read(view), read(view) on second reader with ' +
+   '2 element Uint8Array, respond(3)');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint8Array([1, 2, 3]));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([1, 2, 3]), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // respondWithNewView() should fulfill the *second* read() request
+  byobRequest1.view[0] = 11;
+  byobRequest1.view[1] = 12;
+  byobRequest1.respondWithNewView(byobRequest1.view.subarray(0, 2));
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after respondWithNewView()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11, 12, 6]).subarray(0, 2), 'second result.value');
+
+}, 'ReadableStream with byte source: releaseLock() with pending read(view), read(view) on second reader, respondWithNewView()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint8Array([1, 2, 3]));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([1, 2, 3]), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // enqueue() should fulfill the *second* read() request
+  controller.enqueue(new Uint8Array([11, 12]));
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after enqueue()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11, 12, 6]).subarray(0, 2), 'second result.value');
+
+}, 'ReadableStream with byte source: releaseLock() with pending read(view), read(view) on second reader, enqueue()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint8Array([1, 2, 3]));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([1, 2, 3]), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // close() followed by respond(0) should fulfill the second read()
+  controller.close();
+  byobRequest1.respond(0);
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after respond()');
+
+  const result2 = await read2;
+  assert_true(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([4, 5, 6]).subarray(0, 0), 'second result.value');
+}, 'ReadableStream with byte source: releaseLock() with pending read(view), read(view) on second reader, ' +
+   'close(), respond(0)');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 4,
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader();
+  const read1 = reader1.read();
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array(4), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader();
+  const read2 = reader2.read();
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // respond() should fulfill the *second* read() request
+  byobRequest1.view[0] = 11;
+  byobRequest1.respond(1);
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11, 0, 0, 0]).subarray(0, 1), 'second result.value');
+
+}, 'ReadableStream with byte source: autoAllocateChunkSize, releaseLock() with pending read(), read() on second reader, respond()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 4,
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader();
+  const read1 = reader1.read();
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array(4), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader();
+  const read2 = reader2.read();
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // enqueue() should fulfill the *second* read() request
+  controller.enqueue(new Uint8Array([11]));
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after enqueue()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11]), 'second result.value');
+
+}, 'ReadableStream with byte source: autoAllocateChunkSize, releaseLock() with pending read(), read() on second reader, enqueue()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 4,
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader();
+  const read1 = reader1.read();
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array(4), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // respond() should fulfill the *second* read() request
+  byobRequest1.view[0] = 11;
+  byobRequest1.respond(1);
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11, 5, 6]).subarray(0, 1), 'second result.value');
+
+}, 'ReadableStream with byte source: autoAllocateChunkSize, releaseLock() with pending read(), read(view) on second reader, respond()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 4,
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader();
+  const read1 = reader1.read();
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array(4), 'first byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint8Array([4, 5, 6]));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // enqueue() should fulfill the *second* read() request
+  controller.enqueue(new Uint8Array([11]));
+  const byobRequest2 = controller.byobRequest;
+  assert_equals(byobRequest2, null, 'byobRequest should be null after enqueue()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([11, 5, 6]).subarray(0, 1), 'second result.value');
+
+}, 'ReadableStream with byte source: autoAllocateChunkSize, releaseLock() with pending read(), read(view) on second reader, enqueue()');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint16Array(1));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([0, 0]), 'first byobRequest.view');
+
+  // respond(1) should partially fill the first read(), but not yet fulfill it
+  byobRequest1.view[0] = 0x11;
+  byobRequest1.respond(1);
+  const byobRequest2 = controller.byobRequest;
+  assert_not_equals(byobRequest2, null, 'second byobRequest should exist');
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11, 0]).subarray(1, 2), 'second byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader({ mode: 'byob' });
+  const read2 = reader2.read(new Uint16Array(1));
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  assert_equals(controller.byobRequest, byobRequest2, 'byobRequest should be unchanged');
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11, 0]).subarray(1, 2), 'byobRequest.view should be unchanged');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // second respond(1) should fill the read request and fulfill it
+  byobRequest2.view[0] = 0x22;
+  byobRequest2.respond(1);
+  assert_equals(controller.byobRequest, null, 'byobRequest should be invalidated after second respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  const view2 = result2.value;
+  assert_equals(view2.byteOffset, 0, 'second result.value.byteOffset');
+  assert_equals(view2.byteLength, 2, 'second result.value.byteLength');
+  const dataView2 = new DataView(view2.buffer, view2.byteOffset, view2.byteLength);
+  assert_equals(dataView2.getUint16(0), 0x1122, 'second result.value[0]');
+
+}, 'ReadableStream with byte source: read(view) with 1 element Uint16Array, respond(1), releaseLock(), read(view) on ' +
+   'second reader with 1 element Uint16Array, respond(1)');
+
+promise_test(async t => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start: t.step_func((c) => {
+      controller = c;
+    })
+  });
+  await flushAsyncEvents();
+
+  const reader1 = rs.getReader({ mode: 'byob' });
+  const read1 = reader1.read(new Uint16Array(1));
+  const byobRequest1 = controller.byobRequest;
+  assert_not_equals(byobRequest1, null, 'first byobRequest should exist');
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([0, 0]), 'first byobRequest.view');
+
+  // respond(1) should partially fill the first read(), but not yet fulfill it
+  byobRequest1.view[0] = 0x11;
+  byobRequest1.respond(1);
+  const byobRequest2 = controller.byobRequest;
+  assert_not_equals(byobRequest2, null, 'second byobRequest should exist');
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11, 0]).subarray(1, 2), 'second byobRequest.view');
+
+  // releaseLock() should reject the pending read, but *not* invalidate the BYOB request
+  reader1.releaseLock();
+  const reader2 = rs.getReader();
+  const read2 = reader2.read();
+  assert_not_equals(controller.byobRequest, null, 'byobRequest should not be invalidated after releaseLock()');
+  assert_equals(controller.byobRequest, byobRequest2, 'byobRequest should be unchanged');
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11, 0]).subarray(1, 2), 'byobRequest.view should be unchanged');
+  await promise_rejects_js(t, TypeError, read1, 'pending read must reject after releaseLock()');
+
+  // enqueue() should fulfill the read request and put remaining byte in the queue
+  controller.enqueue(new Uint8Array([0x22]));
+  assert_equals(controller.byobRequest, null, 'byobRequest should be invalidated after second respond()');
+
+  const result2 = await read2;
+  assert_false(result2.done, 'second result.done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x11]), 'second result.value');
+
+  const result3 = await reader2.read();
+  assert_false(result3.done, 'third result.done');
+  assert_typed_array_equals(result3.value, new Uint8Array([0x22]), 'third result.value');
+
+}, 'ReadableStream with byte source: read(view) with 1 element Uint16Array, respond(1), releaseLock(), read() on ' +
+   'second reader, enqueue()');
+
+promise_test(async t => {
+  // Tests https://github.com/nodejs/node/issues/41886
+  const stream = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 10,
+    pull: t.step_func((c) => {
+      const newView = new Uint8Array(c.byobRequest.view.buffer, 0, 3);
+      newView.set([20, 21, 22]);
+      c.byobRequest.respondWithNewView(newView);
+    })
+  });
+
+  const reader = stream.getReader();
+  const result = await reader.read();
+  assert_false(result.done, 'result.done');
+
+  const view = result.value;
+  assert_equals(view.byteOffset, 0, 'result.value.byteOffset');
+  assert_equals(view.byteLength, 3, 'result.value.byteLength');
+  assert_equals(view.buffer.byteLength, 10, 'result.value.buffer.byteLength');
+  assert_array_equals([...new Uint8Array(view)], [20, 21, 22], 'result.value');
+}, 'ReadableStream with byte source: autoAllocateChunkSize, read(), respondWithNewView()');
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/non-transferable-buffers.any.js b/testing/web-platform/tests/streams/readable-byte-streams/non-transferable-buffers.any.js
new file mode 100644
index 0000000000..e8ea3c4f96
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/non-transferable-buffers.any.js
@@ -0,0 +1,58 @@
+// META: global=window,worker
+'use strict';
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const reader = rs.getReader({ mode: 'byob' });
+  const memory = new WebAssembly.Memory({ initial: 1 });
+  const view = new Uint8Array(memory.buffer, 0, 1);
+  await promise_rejects_js(t, TypeError, reader.read(view));
+}, 'ReadableStream with byte source: read() with a non-transferable buffer');
+
+test(t => {
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull: t.unreached_func('pull() should not be called'),
+    type: 'bytes'
+  });
+
+  const memory = new WebAssembly.Memory({ initial: 1 });
+  const view = new Uint8Array(memory.buffer, 0, 1);
+  assert_throws_js(TypeError, () => controller.enqueue(view));
+}, 'ReadableStream with byte source: enqueue() with a non-transferable buffer');
+
+promise_test(async t => {
+  let byobRequest;
+  let resolvePullCalledPromise;
+  const pullCalledPromise = new Promise(resolve => {
+    resolvePullCalledPromise = resolve;
+  });
+  const rs = new ReadableStream({
+    pull(controller) {
+      byobRequest = controller.byobRequest;
+      resolvePullCalledPromise();
+    },
+    type: 'bytes'
+  });
+
+  const memory = new WebAssembly.Memory({ initial: 1 });
+  // Make sure the backing buffers of both views have the same length
+  const byobView = new Uint8Array(new ArrayBuffer(memory.buffer.byteLength), 0, 1);
+  const newView = new Uint8Array(memory.buffer, byobView.byteOffset, byobView.byteLength);
+
+  const reader = rs.getReader({ mode: 'byob' });
+  reader.read(byobView).then(
+    t.unreached_func('read() should not resolve'),
+    t.unreached_func('read() should not reject')
+  );
+  await pullCalledPromise;
+
+  assert_throws_js(TypeError, () => byobRequest.respondWithNewView(newView));
+}, 'ReadableStream with byte source: respondWithNewView() with a non-transferable buffer');
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/respond-after-enqueue.any.js b/testing/web-platform/tests/streams/readable-byte-streams/respond-after-enqueue.any.js
new file mode 100644
index 0000000000..b93cec9739
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/respond-after-enqueue.any.js
@@ -0,0 +1,55 @@
+// META: global=window,worker
+
+'use strict';
+
+// Repro for Blink bug https://crbug.com/1255762.
+promise_test(async () => {
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 10,
+    pull(controller) {
+      controller.enqueue(new Uint8Array([1, 2, 3]));
+      controller.byobRequest.respond(10);
+    }
+  });
+
+  const reader = rs.getReader();
+  const {value, done} = await reader.read();
+  assert_false(done, 'done should not be true');
+  assert_array_equals(value, [1, 2, 3], 'value should be 3 bytes');
+}, 'byobRequest.respond() after enqueue() should not crash');
+
+promise_test(async () => {
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 10,
+    pull(controller) {
+      const byobRequest = controller.byobRequest;
+      controller.enqueue(new Uint8Array([1, 2, 3]));
+      byobRequest.respond(10);
+    }
+  });
+
+  const reader = rs.getReader();
+  const {value, done} = await reader.read();
+  assert_false(done, 'done should not be true');
+  assert_array_equals(value, [1, 2, 3], 'value should be 3 bytes');
+}, 'byobRequest.respond() with cached byobRequest after enqueue() should not crash');
+
+promise_test(async () => {
+  const rs = new ReadableStream({
+    type: 'bytes',
+    autoAllocateChunkSize: 10,
+    pull(controller) {
+      controller.enqueue(new Uint8Array([1, 2, 3]));
+      controller.byobRequest.respond(2);
+    }
+  });
+
+  const reader = rs.getReader();
+  const [read1, read2] = await Promise.all([reader.read(), reader.read()]);
+  assert_false(read1.done, 'read1.done should not be true');
+  assert_array_equals(read1.value, [1, 2, 3], 'read1.value should be 3 bytes');
+  assert_false(read2.done, 'read2.done should not be true');
+  assert_array_equals(read2.value, [0, 0], 'read2.value should be 2 bytes');
+}, 'byobRequest.respond() after enqueue() with double read should not crash');
diff --git a/testing/web-platform/tests/streams/readable-byte-streams/tee.any.js b/testing/web-platform/tests/streams/readable-byte-streams/tee.any.js
new file mode 100644
index 0000000000..85844669cd
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-byte-streams/tee.any.js
@@ -0,0 +1,936 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+// META: script=../resources/rs-test-templates.js
+'use strict';
+
+test(() => {
+
+  const rs = new ReadableStream({ type: 'bytes' });
+  const result = rs.tee();
+
+  assert_true(Array.isArray(result), 'return value should be an array');
+  assert_equals(result.length, 2, 'array should have length 2');
+  assert_equals(result[0].constructor, ReadableStream, '0th element should be a ReadableStream');
+  assert_equals(result[1].constructor, ReadableStream, '1st element should be a ReadableStream');
+
+}, 'ReadableStream teeing with byte source: rs.tee() returns an array of two ReadableStreams');
+
+promise_test(async t => {
+
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+      c.close();
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  reader2.closed.then(t.unreached_func('branch2 should not be closed'));
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'value');
+  }
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x02]), 'value');
+  }
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, true, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0]).subarray(0, 0), 'value');
+  }
+
+  {
+    const result = await reader2.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'value');
+  }
+
+  await reader1.closed;
+
+}, 'ReadableStream teeing with byte source: should be able to read one branch to the end without affecting the other');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const enqueuedChunk = new Uint8Array([0x01]);
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      if (pullCount === 1) {
+        c.enqueue(enqueuedChunk);
+      }
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  const [result1, result2] = await Promise.all([reader1.read(), reader2.read()]);
+  assert_equals(result1.done, false, 'reader1 done');
+  assert_equals(result2.done, false, 'reader2 done');
+
+  const view1 = result1.value;
+  const view2 = result2.value;
+  assert_typed_array_equals(view1, new Uint8Array([0x01]), 'reader1 value');
+  assert_typed_array_equals(view2, new Uint8Array([0x01]), 'reader2 value');
+
+  assert_not_equals(view1.buffer, view2.buffer, 'chunks should have different buffers');
+  assert_not_equals(enqueuedChunk.buffer, view1.buffer, 'enqueued chunk and branch1\'s chunk should have different buffers');
+  assert_not_equals(enqueuedChunk.buffer, view2.buffer, 'enqueued chunk and branch2\'s chunk should have different buffers');
+
+}, 'ReadableStream teeing with byte source: chunks should be cloned for each branch');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      if (pullCount === 1) {
+        c.byobRequest.view[0] = 0x01;
+        c.byobRequest.respond(1);
+      }
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader();
+  const buffer = new Uint8Array([42, 42, 42]).buffer;
+
+  {
+    const result = await reader1.read(new Uint8Array(buffer, 0, 1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01, 42, 42]).subarray(0, 1), 'value');
+  }
+
+  {
+    const result = await reader2.read();
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'value');
+  }
+
+}, 'ReadableStream teeing with byte source: chunks for BYOB requests from branch 1 should be cloned to branch 2');
+
+promise_test(async t => {
+
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+    },
+    pull() {
+      throw theError;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'first read from branch1 should not be done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'first read from branch1');
+  }
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'second read from branch1 should not be done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x02]), 'second read from branch1');
+  }
+
+  await promise_rejects_exactly(t, theError, reader1.read(new Uint8Array(1)));
+  await promise_rejects_exactly(t, theError, reader2.read(new Uint8Array(1)));
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+}, 'ReadableStream teeing with byte source: errors in the source should propagate to both branches');
+
+promise_test(async () => {
+
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+      c.close();
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  branch1.cancel();
+
+  const [chunks1, chunks2] = await Promise.all([readableStreamToArray(branch1), readableStreamToArray(branch2)]);
+  assert_array_equals(chunks1, [], 'branch1 should have no chunks');
+  assert_equals(chunks2.length, 2, 'branch2 should have two chunks');
+  assert_typed_array_equals(chunks2[0], new Uint8Array([0x01]), 'first chunk from branch2');
+  assert_typed_array_equals(chunks2[1], new Uint8Array([0x02]), 'second chunk from branch2');
+
+}, 'ReadableStream teeing with byte source: canceling branch1 should not impact branch2');
+
+promise_test(async () => {
+
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+      c.close();
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  branch2.cancel();
+
+  const [chunks1, chunks2] = await Promise.all([readableStreamToArray(branch1), readableStreamToArray(branch2)]);
+  assert_equals(chunks1.length, 2, 'branch1 should have two chunks');
+  assert_typed_array_equals(chunks1[0], new Uint8Array([0x01]), 'first chunk from branch1');
+  assert_typed_array_equals(chunks1[1], new Uint8Array([0x02]), 'second chunk from branch1');
+  assert_array_equals(chunks2, [], 'branch2 should have no chunks');
+
+}, 'ReadableStream teeing with byte source: canceling branch2 should not impact branch1');
+
+templatedRSTeeCancel('ReadableStream teeing with byte source', (extras) => {
+  return new ReadableStream({ type: 'bytes', ...extras });
+});
+
+promise_test(async () => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  const promise = Promise.all([reader1.closed, reader2.closed]);
+
+  controller.close();
+
+  // The branches are created with HWM 0, so we need to read from at least one of them
+  // to observe the stream becoming closed.
+  const read1 = await reader1.read(new Uint8Array(1));
+  assert_equals(read1.done, true, 'first read from branch1 should be done');
+
+  await promise;
+
+}, 'ReadableStream teeing with byte source: closing the original should close the branches');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+  controller.error(theError);
+  await promise;
+
+}, 'ReadableStream teeing with byte source: erroring the original should immediately error the branches');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read()),
+    promise_rejects_exactly(t, theError, reader2.read())
+  ]);
+
+  controller.error(theError);
+  await promise;
+
+}, 'ReadableStream teeing with byte source: erroring the original should error pending reads from default reader');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read(new Uint8Array(1))),
+    promise_rejects_exactly(t, theError, reader2.read(new Uint8Array(1)))
+  ]);
+
+  controller.error(theError);
+  await promise;
+
+}, 'ReadableStream teeing with byte source: erroring the original should error pending reads from BYOB reader');
+
+promise_test(async () => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+  const cancelPromise = reader2.cancel();
+
+  controller.enqueue(new Uint8Array([0x01]));
+
+  const read1 = await reader1.read(new Uint8Array(1));
+  assert_equals(read1.done, false, 'first read() from branch1 should not be done');
+  assert_typed_array_equals(read1.value, new Uint8Array([0x01]), 'first read() from branch1');
+
+  controller.close();
+
+  const read2 = await reader1.read(new Uint8Array(1));
+  assert_equals(read2.done, true, 'second read() from branch1 should be done');
+
+  await Promise.all([
+    reader1.closed,
+    cancelPromise
+  ]);
+
+}, 'ReadableStream teeing with byte source: canceling branch1 should finish when branch2 reads until end of stream');
+
+promise_test(async t => {
+
+  let controller;
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+  const cancelPromise = reader2.cancel();
+
+  controller.error(theError);
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read(new Uint8Array(1))),
+    cancelPromise
+  ]);
+
+}, 'ReadableStream teeing with byte source: canceling branch1 should finish when original stream errors');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  // Create two branches, each with a HWM of 0. This should result in no chunks being pulled.
+  rs.tee();
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, [], 'pull should not be called');
+
+}, 'ReadableStream teeing with byte source: should not pull any chunks if no branches are reading');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({
+    type: 'bytes',
+    pull(controller) {
+      controller.enqueue(new Uint8Array([0x01]));
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+  await Promise.all([
+    reader1.read(new Uint8Array(1)),
+    reader2.read(new Uint8Array(1))
+  ]);
+  assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+}, 'ReadableStream teeing with byte source: should only pull enough to fill the emptiest queue');
+
+promise_test(async t => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const theError = { name: 'boo!' };
+
+  rs.controller.error(theError);
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, [], 'pull should not be called');
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+}, 'ReadableStream teeing with byte source: should not pull when original is already errored');
+
+for (const branch of [1, 2]) {
+  promise_test(async t => {
+
+    const rs = recordingReadableStream({ type: 'bytes' });
+    const theError = { name: 'boo!' };
+
+    const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+    await flushAsyncEvents();
+    assert_array_equals(rs.events, [], 'pull should not be called');
+
+    const reader = (branch === 1) ? reader1 : reader2;
+    const read1 = reader.read(new Uint8Array(1));
+
+    await flushAsyncEvents();
+    assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+    rs.controller.error(theError);
+
+    await Promise.all([
+      promise_rejects_exactly(t, theError, read1),
+      promise_rejects_exactly(t, theError, reader1.closed),
+      promise_rejects_exactly(t, theError, reader2.closed)
+    ]);
+
+    await flushAsyncEvents();
+    assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+  }, `ReadableStream teeing with byte source: stops pulling when original stream errors while branch ${branch} is reading`);
+}
+
+promise_test(async t => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const theError = { name: 'boo!' };
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, [], 'pull should not be called');
+
+  const read1 = reader1.read(new Uint8Array(1));
+  const read2 = reader2.read(new Uint8Array(1));
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+  rs.controller.error(theError);
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, read1),
+    promise_rejects_exactly(t, theError, read2),
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+}, 'ReadableStream teeing with byte source: stops pulling when original stream errors while both branches are reading');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  const read2 = reader2.read(new Uint8Array([0x22]));
+
+  const cancel1 = reader1.cancel();
+  await flushAsyncEvents();
+  const cancel2 = reader2.cancel();
+
+  const result1 = await read1;
+  assert_object_equals(result1, { value: undefined, done: true });
+  const result2 = await read2;
+  assert_object_equals(result2, { value: undefined, done: true });
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing with byte source: canceling both branches in sequence with delay');
+
+promise_test(async t => {
+
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    type: 'bytes',
+    cancel() {
+      throw theError;
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  const read2 = reader2.read(new Uint8Array([0x22]));
+
+  const cancel1 = reader1.cancel();
+  await flushAsyncEvents();
+  const cancel2 = reader2.cancel();
+
+  const result1 = await read1;
+  assert_object_equals(result1, { value: undefined, done: true });
+  const result2 = await read2;
+  assert_object_equals(result2, { value: undefined, done: true });
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, cancel1),
+    promise_rejects_exactly(t, theError, cancel2)
+  ]);
+
+}, 'ReadableStream teeing with byte source: failing to cancel when canceling both branches in sequence with delay');
+
+promise_test(async () => {
+
+  let cancelResolve;
+  const cancelCalled = new Promise((resolve) => {
+    cancelResolve = resolve;
+  });
+  const rs = recordingReadableStream({
+    type: 'bytes',
+    cancel() {
+      cancelResolve();
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  const byobRequest1 = rs.controller.byobRequest;
+  assert_not_equals(byobRequest1, null);
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([0x11]), 'byobRequest1.view');
+
+  // Cancelling branch1 should not affect the BYOB request.
+  const cancel1 = reader1.cancel();
+  const result1 = await read1;
+  assert_equals(result1.done, true);
+  assert_equals(result1.value, undefined);
+  await flushAsyncEvents();
+  const byobRequest2 = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11]), 'byobRequest2.view');
+
+  // Cancelling branch1 should invalidate the BYOB request.
+  const cancel2 = reader2.cancel();
+  await cancelCalled;
+  const byobRequest3 = rs.controller.byobRequest;
+  assert_equals(byobRequest3, null);
+  const result2 = await read2;
+  assert_equals(result2.done, true);
+  assert_equals(result2.value, undefined);
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch1, cancel branch2');
+
+promise_test(async () => {
+
+  let cancelResolve;
+  const cancelCalled = new Promise((resolve) => {
+    cancelResolve = resolve;
+  });
+  const rs = recordingReadableStream({
+    type: 'bytes',
+    cancel() {
+      cancelResolve();
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  const byobRequest1 = rs.controller.byobRequest;
+  assert_not_equals(byobRequest1, null);
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([0x11]), 'byobRequest1.view');
+
+  // Cancelling branch2 should not affect the BYOB request.
+  const cancel2 = reader2.cancel();
+  const result2 = await read2;
+  assert_equals(result2.done, true);
+  assert_equals(result2.value, undefined);
+  await flushAsyncEvents();
+  const byobRequest2 = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11]), 'byobRequest2.view');
+
+  // Cancelling branch1 should invalidate the BYOB request.
+  const cancel1 = reader1.cancel();
+  await cancelCalled;
+  const byobRequest3 = rs.controller.byobRequest;
+  assert_equals(byobRequest3, null);
+  const result1 = await read1;
+  assert_equals(result1.done, true);
+  assert_equals(result1.value, undefined);
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch2, cancel branch1');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'first byobRequest.view');
+
+  // Cancelling branch2 should not affect the BYOB request.
+  reader2.cancel();
+  const result2 = await read2;
+  assert_equals(result2.done, true);
+  assert_equals(result2.value, undefined);
+  await flushAsyncEvents();
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'second byobRequest.view');
+
+  // Respond to the BYOB request.
+  rs.controller.byobRequest.view[0] = 0x33;
+  rs.controller.byobRequest.respond(1);
+
+  // branch1 should receive the read chunk.
+  const result1 = await read1;
+  assert_equals(result1.done, false);
+  assert_typed_array_equals(result1.value, new Uint8Array([0x33]), 'first read() from branch1');
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch2, enqueue to branch1');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'first byobRequest.view');
+
+  // Cancelling branch1 should not affect the BYOB request.
+  reader1.cancel();
+  const result1 = await read1;
+  assert_equals(result1.done, true);
+  assert_equals(result1.value, undefined);
+  await flushAsyncEvents();
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'second byobRequest.view');
+
+  // Respond to the BYOB request.
+  rs.controller.byobRequest.view[0] = 0x33;
+  rs.controller.byobRequest.respond(1);
+
+  // branch2 should receive the read chunk.
+  const result2 = await read2;
+  assert_equals(result2.done, false);
+  assert_typed_array_equals(result2.value, new Uint8Array([0x33]), 'first read() from branch2');
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch1, respond to branch2');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const byobRequestDefined = [];
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      byobRequestDefined.push(c.byobRequest !== null);
+      c.enqueue(new Uint8Array([pullCount]));
+    }
+  });
+
+  const [branch1, _] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+
+  const result1 = await reader1.read(new Uint8Array([0x11]));
+  assert_equals(result1.done, false, 'first read should not be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x1]), 'first read');
+  assert_equals(pullCount, 1, 'pull() should be called once');
+  assert_equals(byobRequestDefined[0], true, 'should have created a BYOB request for first read');
+
+  reader1.releaseLock();
+  const reader2 = branch1.getReader();
+
+  const result2 = await reader2.read();
+  assert_equals(result2.done, false, 'second read should not be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x2]), 'second read');
+  assert_equals(pullCount, 2, 'pull() should be called twice');
+  assert_equals(byobRequestDefined[1], false, 'should not have created a BYOB request for second read');
+
+}, 'ReadableStream teeing with byte source: pull with BYOB reader, then pull with default reader');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const byobRequestDefined = [];
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      byobRequestDefined.push(c.byobRequest !== null);
+      c.enqueue(new Uint8Array([pullCount]));
+    }
+  });
+
+  const [branch1, _] = rs.tee();
+  const reader1 = branch1.getReader();
+
+  const result1 = await reader1.read();
+  assert_equals(result1.done, false, 'first read should not be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x1]), 'first read');
+  assert_equals(pullCount, 1, 'pull() should be called once');
+  assert_equals(byobRequestDefined[0], false, 'should not have created a BYOB request for first read');
+
+  reader1.releaseLock();
+  const reader2 = branch1.getReader({ mode: 'byob' });
+
+  const result2 = await reader2.read(new Uint8Array([0x22]));
+  assert_equals(result2.done, false, 'second read should not be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x2]), 'second read');
+  assert_equals(pullCount, 2, 'pull() should be called twice');
+  assert_equals(byobRequestDefined[1], true, 'should have created a BYOB request for second read');
+
+}, 'ReadableStream teeing with byte source: pull with default reader, then pull with BYOB reader');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({
+    type: 'bytes'
+  });
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  // Wait for each branch's start() promise to resolve.
+  await flushAsyncEvents();
+
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+
+  // branch2 should provide the BYOB request.
+  const byobRequest = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest.view, new Uint8Array([0x22]), 'first BYOB request');
+  byobRequest.view[0] = 0x01;
+  byobRequest.respond(1);
+
+  const result1 = await read1;
+  assert_equals(result1.done, false, 'first read should not be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x1]), 'first read');
+
+  const result2 = await read2;
+  assert_equals(result2.done, false, 'second read should not be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x1]), 'second read');
+
+}, 'ReadableStream teeing with byte source: read from branch2, then read from branch1');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader({ mode: 'byob' });
+  await flushAsyncEvents();
+
+  const read1 = reader1.read();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // There should be no BYOB request.
+  assert_equals(rs.controller.byobRequest, null, 'first BYOB request');
+
+  // Close the stream.
+  rs.controller.close();
+
+  const result1 = await read1;
+  assert_equals(result1.done, true, 'read from branch1 should be done');
+  assert_equals(result1.value, undefined, 'read from branch1');
+
+  // branch2 should get its buffer back.
+  const result2 = await read2;
+  assert_equals(result2.done, true, 'read from branch2 should be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x22]).subarray(0, 0), 'read from branch2');
+
+}, 'ReadableStream teeing with byte source: read from branch1 with default reader, then close while branch2 has pending BYOB read');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader();
+  await flushAsyncEvents();
+
+  const read2 = reader2.read();
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+
+  // There should be no BYOB request.
+  assert_equals(rs.controller.byobRequest, null, 'first BYOB request');
+
+  // Close the stream.
+  rs.controller.close();
+
+  const result2 = await read2;
+  assert_equals(result2.done, true, 'read from branch2 should be done');
+  assert_equals(result2.value, undefined, 'read from branch2');
+
+  // branch1 should get its buffer back.
+  const result1 = await read1;
+  assert_equals(result1.done, true, 'read from branch1 should be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]).subarray(0, 0), 'read from branch1');
+
+}, 'ReadableStream teeing with byte source: read from branch2 with default reader, then close while branch1 has pending BYOB read');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+  await flushAsyncEvents();
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // branch1 should provide the BYOB request.
+  const byobRequest = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest.view, new Uint8Array([0x11]), 'first BYOB request');
+
+  // Close the stream.
+  rs.controller.close();
+  byobRequest.respond(0);
+
+  // Both branches should get their buffers back.
+  const result1 = await read1;
+  assert_equals(result1.done, true, 'first read should be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]).subarray(0, 0), 'first read');
+
+  const result2 = await read2;
+  assert_equals(result2.done, true, 'second read should be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x22]).subarray(0, 0), 'second read');
+
+}, 'ReadableStream teeing with byte source: close when both branches have pending BYOB reads');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+  const branch1Reads = [reader1.read(), reader1.read()];
+  const branch2Reads = [reader2.read(), reader2.read()];
+
+  await flushAsyncEvents();
+  rs.controller.enqueue(new Uint8Array([0x11]));
+  rs.controller.close();
+
+  const result1 = await branch1Reads[0];
+  assert_equals(result1.done, false, 'first read() from branch1 should be not done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]), 'first chunk from branch1 should be correct');
+  const result2 = await branch2Reads[0];
+  assert_equals(result2.done, false, 'first read() from branch2 should be not done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x11]), 'first chunk from branch2 should be correct');
+
+  assert_object_equals(await branch1Reads[1], { value: undefined, done: true }, 'second read() from branch1 should be done');
+  assert_object_equals(await branch2Reads[1], { value: undefined, done: true }, 'second read() from branch2 should be done');
+
+}, 'ReadableStream teeing with byte source: enqueue() and close() while both branches are pulling');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+  const branch1Reads = [reader1.read(new Uint8Array(1)), reader1.read(new Uint8Array(1))];
+  const branch2Reads = [reader2.read(new Uint8Array(1)), reader2.read(new Uint8Array(1))];
+
+  await flushAsyncEvents();
+  rs.controller.byobRequest.view[0] = 0x11;
+  rs.controller.byobRequest.respond(1);
+  rs.controller.close();
+
+  const result1 = await branch1Reads[0];
+  assert_equals(result1.done, false, 'first read() from branch1 should be not done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]), 'first chunk from branch1 should be correct');
+  const result2 = await branch2Reads[0];
+  assert_equals(result2.done, false, 'first read() from branch2 should be not done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x11]), 'first chunk from branch2 should be correct');
+
+  const result3 = await branch1Reads[1];
+  assert_equals(result3.done, true, 'second read() from branch1 should be done');
+  assert_typed_array_equals(result3.value, new Uint8Array([0]).subarray(0, 0), 'second chunk from branch1 should be correct');
+  const result4 = await branch2Reads[1];
+  assert_equals(result4.done, true, 'second read() from branch2 should be done');
+  assert_typed_array_equals(result4.value, new Uint8Array([0]).subarray(0, 0), 'second chunk from branch2 should be correct');
+
+}, 'ReadableStream teeing with byte source: respond() and close() while both branches are pulling');
diff --git a/testing/web-platform/tests/streams/readable-streams/async-iterator.any.js b/testing/web-platform/tests/streams/readable-streams/async-iterator.any.js
new file mode 100644
index 0000000000..3ccaca17bc
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/async-iterator.any.js
@@ -0,0 +1,650 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1');
+
+function assert_iter_result(iterResult, value, done, message) {
+  const prefix = message === undefined ? '' : `${message} `;
+  assert_equals(typeof iterResult, 'object', `${prefix}type is object`);
+  assert_equals(Object.getPrototypeOf(iterResult), Object.prototype, `${prefix}[[Prototype]]`);
+  assert_array_equals(Object.getOwnPropertyNames(iterResult).sort(), ['done', 'value'], `${prefix}property names`);
+  assert_equals(iterResult.value, value, `${prefix}value`);
+  assert_equals(iterResult.done, done, `${prefix}done`);
+}
+
+test(() => {
+  const s = new ReadableStream();
+  const it = s.values();
+  const proto = Object.getPrototypeOf(it);
+
+  const AsyncIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf(async function* () {}).prototype);
+  assert_equals(Object.getPrototypeOf(proto), AsyncIteratorPrototype, 'prototype should extend AsyncIteratorPrototype');
+
+  const methods = ['next', 'return'].sort();
+  assert_array_equals(Object.getOwnPropertyNames(proto).sort(), methods, 'should have all the correct methods');
+
+  for (const m of methods) {
+    const propDesc = Object.getOwnPropertyDescriptor(proto, m);
+    assert_true(propDesc.enumerable, 'method should be enumerable');
+    assert_true(propDesc.configurable, 'method should be configurable');
+    assert_true(propDesc.writable, 'method should be writable');
+    assert_equals(typeof it[m], 'function', 'method should be a function');
+    assert_equals(it[m].name, m, 'method should have the correct name');
+  }
+
+  assert_equals(it.next.length, 0, 'next should have no parameters');
+  assert_equals(it.return.length, 1, 'return should have 1 parameter');
+  assert_equals(typeof it.throw, 'undefined', 'throw should not exist');
+}, 'Async iterator instances should have the correct list of properties');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(1);
+      c.enqueue(2);
+      c.enqueue(3);
+      c.close();
+    }
+  });
+
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, [1, 2, 3]);
+}, 'Async-iterating a push source');
+
+promise_test(async () => {
+  let i = 1;
+  const s = new ReadableStream({
+    pull(c) {
+      c.enqueue(i);
+      if (i >= 3) {
+        c.close();
+      }
+      i += 1;
+    }
+  });
+
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, [1, 2, 3]);
+}, 'Async-iterating a pull source');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(undefined);
+      c.enqueue(undefined);
+      c.enqueue(undefined);
+      c.close();
+    }
+  });
+
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, [undefined, undefined, undefined]);
+}, 'Async-iterating a push source with undefined values');
+
+promise_test(async () => {
+  let i = 1;
+  const s = new ReadableStream({
+    pull(c) {
+      c.enqueue(undefined);
+      if (i >= 3) {
+        c.close();
+      }
+      i += 1;
+    }
+  });
+
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, [undefined, undefined, undefined]);
+}, 'Async-iterating a pull source with undefined values');
+
+promise_test(async () => {
+  let i = 1;
+  const s = recordingReadableStream({
+    pull(c) {
+      c.enqueue(i);
+      if (i >= 3) {
+        c.close();
+      }
+      i += 1;
+    },
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const it = s.values();
+  assert_array_equals(s.events, []);
+
+  const read1 = await it.next();
+  assert_iter_result(read1, 1, false);
+  assert_array_equals(s.events, ['pull']);
+
+  const read2 = await it.next();
+  assert_iter_result(read2, 2, false);
+  assert_array_equals(s.events, ['pull', 'pull']);
+
+  const read3 = await it.next();
+  assert_iter_result(read3, 3, false);
+  assert_array_equals(s.events, ['pull', 'pull', 'pull']);
+
+  const read4 = await it.next();
+  assert_iter_result(read4, undefined, true);
+  assert_array_equals(s.events, ['pull', 'pull', 'pull']);
+}, 'Async-iterating a pull source manually');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.error('e');
+    },
+  });
+
+  try {
+    for await (const chunk of s) {}
+    assert_unreached();
+  } catch (e) {
+    assert_equals(e, 'e');
+  }
+}, 'Async-iterating an errored stream throws');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+
+  for await (const chunk of s) {
+    assert_unreached();
+  }
+}, 'Async-iterating a closed stream never executes the loop body, but works fine');
+
+promise_test(async () => {
+  const s = new ReadableStream();
+
+  const loop = async () => {
+    for await (const chunk of s) {
+      assert_unreached();
+    }
+    assert_unreached();
+  };
+
+  await Promise.race([
+    loop(),
+    flushAsyncEvents()
+  ]);
+}, 'Async-iterating an empty but not closed/errored stream never executes the loop body and stalls the async function');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(1);
+      c.enqueue(2);
+      c.enqueue(3);
+      c.close();
+    },
+  });
+
+  const reader = s.getReader();
+  const readResult = await reader.read();
+  assert_iter_result(readResult, 1, false);
+  reader.releaseLock();
+
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, [2, 3]);
+}, 'Async-iterating a partially consumed stream');
+
+for (const type of ['throw', 'break', 'return']) {
+  for (const preventCancel of [false, true]) {
+    promise_test(async () => {
+      const s = recordingReadableStream({
+        start(c) {
+          c.enqueue(0);
+        }
+      });
+
+      // use a separate function for the loop body so return does not stop the test
+      const loop = async () => {
+        for await (const c of s.values({ preventCancel })) {
+          if (type === 'throw') {
+            throw new Error();
+          } else if (type === 'break') {
+            break;
+          } else if (type === 'return') {
+            return;
+          }
+        }
+      };
+
+      try {
+        await loop();
+      } catch (e) {}
+
+      if (preventCancel) {
+        assert_array_equals(s.events, ['pull'], `cancel() should not be called`);
+      } else {
+        assert_array_equals(s.events, ['pull', 'cancel', undefined], `cancel() should be called`);
+      }
+    }, `Cancellation behavior when ${type}ing inside loop body; preventCancel = ${preventCancel}`);
+  }
+}
+
+for (const preventCancel of [false, true]) {
+  promise_test(async () => {
+    const s = recordingReadableStream({
+      start(c) {
+        c.enqueue(0);
+      }
+    });
+
+    const it = s.values({ preventCancel });
+    await it.return();
+
+    if (preventCancel) {
+      assert_array_equals(s.events, [], `cancel() should not be called`);
+    } else {
+      assert_array_equals(s.events, ['cancel', undefined], `cancel() should be called`);
+    }
+  }, `Cancellation behavior when manually calling return(); preventCancel = ${preventCancel}`);
+}
+
+promise_test(async t => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResult1 = await it.next();
+  assert_iter_result(iterResult1, 0, false, '1st next()');
+
+  await promise_rejects_exactly(t, error1, it.next(), '2nd next()');
+}, 'next() rejects if the stream errors');
+
+promise_test(async () => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResult = await it.return('return value');
+  assert_iter_result(iterResult, 'return value', true);
+}, 'return() does not rejects if the stream has not errored yet');
+
+promise_test(async t => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      // Do not error in start() because doing so would prevent acquiring a reader/async iterator.
+      c.error(error1);
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  await flushAsyncEvents();
+  await promise_rejects_exactly(t, error1, it.return('return value'));
+}, 'return() rejects if the stream has errored');
+
+promise_test(async t => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResult1 = await it.next();
+  assert_iter_result(iterResult1, 0, false, '1st next()');
+
+  await promise_rejects_exactly(t, error1, it.next(), '2nd next()');
+
+  const iterResult3 = await it.next();
+  assert_iter_result(iterResult3, undefined, true, '3rd next()');
+}, 'next() that succeeds; next() that reports an error; next()');
+
+promise_test(async () => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResults = await Promise.allSettled([it.next(), it.next(), it.next()]);
+
+  assert_equals(iterResults[0].status, 'fulfilled', '1st next() promise status');
+  assert_iter_result(iterResults[0].value, 0, false, '1st next()');
+
+  assert_equals(iterResults[1].status, 'rejected', '2nd next() promise status');
+  assert_equals(iterResults[1].reason, error1, '2nd next() rejection reason');
+
+  assert_equals(iterResults[2].status, 'fulfilled', '3rd next() promise status');
+  assert_iter_result(iterResults[2].value, undefined, true, '3rd next()');
+}, 'next() that succeeds; next() that reports an error(); next() [no awaiting]');
+
+promise_test(async t => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResult1 = await it.next();
+  assert_iter_result(iterResult1, 0, false, '1st next()');
+
+  await promise_rejects_exactly(t, error1, it.next(), '2nd next()');
+
+  const iterResult3 = await it.return('return value');
+  assert_iter_result(iterResult3, 'return value', true, 'return()');
+}, 'next() that succeeds; next() that reports an error(); return()');
+
+promise_test(async () => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResults = await Promise.allSettled([it.next(), it.next(), it.return('return value')]);
+
+  assert_equals(iterResults[0].status, 'fulfilled', '1st next() promise status');
+  assert_iter_result(iterResults[0].value, 0, false, '1st next()');
+
+  assert_equals(iterResults[1].status, 'rejected', '2nd next() promise status');
+  assert_equals(iterResults[1].reason, error1, '2nd next() rejection reason');
+
+  assert_equals(iterResults[2].status, 'fulfilled', 'return() promise status');
+  assert_iter_result(iterResults[2].value, 'return value', true, 'return()');
+}, 'next() that succeeds; next() that reports an error(); return() [no awaiting]');
+
+promise_test(async () => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      c.enqueue(timesPulled);
+      ++timesPulled;
+    }
+  });
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResult1 = await it.next();
+  assert_iter_result(iterResult1, 0, false, 'next()');
+
+  const iterResult2 = await it.return('return value');
+  assert_iter_result(iterResult2, 'return value', true, 'return()');
+
+  assert_equals(timesPulled, 2);
+}, 'next() that succeeds; return()');
+
+promise_test(async () => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      c.enqueue(timesPulled);
+      ++timesPulled;
+    }
+  });
+  const it = s[Symbol.asyncIterator]();
+
+  const iterResults = await Promise.allSettled([it.next(), it.return('return value')]);
+
+  assert_equals(iterResults[0].status, 'fulfilled', 'next() promise status');
+  assert_iter_result(iterResults[0].value, 0, false, 'next()');
+
+  assert_equals(iterResults[1].status, 'fulfilled', 'return() promise status');
+  assert_iter_result(iterResults[1].value, 'return value', true, 'return()');
+
+  assert_equals(timesPulled, 2);
+}, 'next() that succeeds; return() [no awaiting]');
+
+promise_test(async () => {
+  const rs = new ReadableStream();
+  const it = rs.values();
+
+  const iterResult1 = await it.return('return value');
+  assert_iter_result(iterResult1, 'return value', true, 'return()');
+
+  const iterResult2 = await it.next();
+  assert_iter_result(iterResult2, undefined, true, 'next()');
+}, 'return(); next()');
+
+promise_test(async () => {
+  const rs = new ReadableStream();
+  const it = rs.values();
+
+  const iterResults = await Promise.allSettled([it.return('return value'), it.next()]);
+
+  assert_equals(iterResults[0].status, 'fulfilled', 'return() promise status');
+  assert_iter_result(iterResults[0].value, 'return value', true, 'return()');
+
+  assert_equals(iterResults[1].status, 'fulfilled', 'next() promise status');
+  assert_iter_result(iterResults[1].value, undefined, true, 'next()');
+}, 'return(); next() [no awaiting]');
+
+promise_test(async () => {
+  const rs = new ReadableStream();
+  const it = rs.values();
+
+  const iterResult1 = await it.return('return value 1');
+  assert_iter_result(iterResult1, 'return value 1', true, '1st return()');
+
+  const iterResult2 = await it.return('return value 2');
+  assert_iter_result(iterResult2, 'return value 2', true, '1st return()');
+}, 'return(); return()');
+
+promise_test(async () => {
+  const rs = new ReadableStream();
+  const it = rs.values();
+
+  const iterResults = await Promise.allSettled([it.return('return value 1'), it.return('return value 2')]);
+
+  assert_equals(iterResults[0].status, 'fulfilled', '1st return() promise status');
+  assert_iter_result(iterResults[0].value, 'return value 1', true, '1st return()');
+
+  assert_equals(iterResults[1].status, 'fulfilled', '2nd return() promise status');
+  assert_iter_result(iterResults[1].value, 'return value 2', true, '1st return()');
+}, 'return(); return() [no awaiting]');
+
+test(() => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(0);
+      c.close();
+    },
+  });
+  s.values();
+  assert_throws_js(TypeError, () => s.values(), 'values() should throw');
+}, 'values() throws if there\'s already a lock');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(1);
+      c.enqueue(2);
+      c.enqueue(3);
+      c.close();
+    }
+  });
+
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, [1, 2, 3]);
+
+  const reader = s.getReader();
+  await reader.closed;
+}, 'Acquiring a reader after exhaustively async-iterating a stream');
+
+promise_test(async t => {
+  let timesPulled = 0;
+  const s = new ReadableStream({
+    pull(c) {
+      if (timesPulled === 0) {
+        c.enqueue(0);
+        ++timesPulled;
+      } else {
+        c.error(error1);
+      }
+    }
+  });
+
+  const it = s[Symbol.asyncIterator]({ preventCancel: true });
+
+  const iterResult1 = await it.next();
+  assert_iter_result(iterResult1, 0, false, '1st next()');
+
+  await promise_rejects_exactly(t, error1, it.next(), '2nd next()');
+
+  const iterResult2 = await it.return('return value');
+  assert_iter_result(iterResult2, 'return value', true, 'return()');
+
+  // i.e. it should not reject with a generic "this stream is locked" TypeError.
+  const reader = s.getReader();
+  await promise_rejects_exactly(t, error1, reader.closed, 'closed on the new reader should reject with the error');
+}, 'Acquiring a reader after return()ing from a stream that errors');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(1);
+      c.enqueue(2);
+      c.enqueue(3);
+      c.close();
+    },
+  });
+
+  // read the first two chunks, then cancel
+  const chunks = [];
+  for await (const chunk of s) {
+    chunks.push(chunk);
+    if (chunk >= 2) {
+      break;
+    }
+  }
+  assert_array_equals(chunks, [1, 2]);
+
+  const reader = s.getReader();
+  await reader.closed;
+}, 'Acquiring a reader after partially async-iterating a stream');
+
+promise_test(async () => {
+  const s = new ReadableStream({
+    start(c) {
+      c.enqueue(1);
+      c.enqueue(2);
+      c.enqueue(3);
+      c.close();
+    },
+  });
+
+  // read the first two chunks, then release lock
+  const chunks = [];
+  for await (const chunk of s.values({preventCancel: true})) {
+    chunks.push(chunk);
+    if (chunk >= 2) {
+      break;
+    }
+  }
+  assert_array_equals(chunks, [1, 2]);
+
+  const reader = s.getReader();
+  const readResult = await reader.read();
+  assert_iter_result(readResult, 3, false);
+  await reader.closed;
+}, 'Acquiring a reader and reading the remaining chunks after partially async-iterating a stream with preventCancel = true');
+
+for (const preventCancel of [false, true]) {
+  test(() => {
+    const rs = new ReadableStream();
+    rs.values({ preventCancel }).return();
+    // The test passes if this line doesn't throw.
+    rs.getReader();
+  }, `return() should unlock the stream synchronously when preventCancel = ${preventCancel}`);
+}
+
+promise_test(async () => {
+  const rs = new ReadableStream({
+    async start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.enqueue('c');
+      await flushAsyncEvents();
+      // At this point, the async iterator has a read request in the stream's queue for its pending next() promise.
+      // Closing the stream now causes two things to happen *synchronously*:
+      //  1. ReadableStreamClose resolves reader.[[closedPromise]] with undefined.
+      //  2. ReadableStreamClose calls the read request's close steps, which calls ReadableStreamReaderGenericRelease,
+      //     which replaces reader.[[closedPromise]] with a rejected promise.
+      c.close();
+    }
+  });
+
+  const chunks = [];
+  for await (const chunk of rs) {
+    chunks.push(chunk);
+  }
+  assert_array_equals(chunks, ['a', 'b', 'c']);
+}, 'close() while next() is pending');
diff --git a/testing/web-platform/tests/streams/readable-streams/bad-strategies.any.js b/testing/web-platform/tests/streams/readable-streams/bad-strategies.any.js
new file mode 100644
index 0000000000..521fbffe3a
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/bad-strategies.any.js
@@ -0,0 +1,159 @@
+// META: global=window,worker
+'use strict';
+
+test(() => {
+
+  const theError = new Error('a unique string');
+
+  assert_throws_exactly(theError, () => {
+    new ReadableStream({}, {
+      get size() {
+        throw theError;
+      },
+      highWaterMark: 5
+    });
+  }, 'construction should re-throw the error');
+
+}, 'Readable stream: throwing strategy.size getter');
+
+promise_test(t => {
+
+  const controllerError = { name: 'controller error' };
+  const thrownError = { name: 'thrown error' };
+
+  let controller;
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        controller = c;
+      }
+    },
+    {
+      size() {
+        controller.error(controllerError);
+        throw thrownError;
+      },
+      highWaterMark: 5
+    }
+  );
+
+  assert_throws_exactly(thrownError, () => controller.enqueue('a'), 'enqueue should re-throw the error');
+
+  return promise_rejects_exactly(t, controllerError, rs.getReader().closed);
+
+}, 'Readable stream: strategy.size errors the stream and then throws');
+
+promise_test(t => {
+
+  const theError = { name: 'my error' };
+
+  let controller;
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        controller = c;
+      }
+    },
+    {
+      size() {
+        controller.error(theError);
+        return Infinity;
+      },
+      highWaterMark: 5
+    }
+  );
+
+  assert_throws_js(RangeError, () => controller.enqueue('a'), 'enqueue should throw a RangeError');
+
+  return promise_rejects_exactly(t, theError, rs.getReader().closed, 'closed should reject with the error');
+
+}, 'Readable stream: strategy.size errors the stream and then returns Infinity');
+
+promise_test(() => {
+
+  const theError = new Error('a unique string');
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        assert_throws_exactly(theError, () => c.enqueue('a'), 'enqueue should throw the error');
+      }
+    },
+    {
+      size() {
+        throw theError;
+      },
+      highWaterMark: 5
+    }
+  );
+
+  return rs.getReader().closed.catch(e => {
+    assert_equals(e, theError, 'closed should reject with the error');
+  });
+
+}, 'Readable stream: throwing strategy.size method');
+
+test(() => {
+
+  const theError = new Error('a unique string');
+
+  assert_throws_exactly(theError, () => {
+    new ReadableStream({}, {
+      size() {
+        return 1;
+      },
+      get highWaterMark() {
+        throw theError;
+      }
+    });
+  }, 'construction should re-throw the error');
+
+}, 'Readable stream: throwing strategy.highWaterMark getter');
+
+test(() => {
+
+  for (const highWaterMark of [-1, -Infinity, NaN, 'foo', {}]) {
+    assert_throws_js(RangeError, () => {
+      new ReadableStream({}, {
+        size() {
+          return 1;
+        },
+        highWaterMark
+      });
+    }, 'construction should throw a RangeError for ' + highWaterMark);
+  }
+
+}, 'Readable stream: invalid strategy.highWaterMark');
+
+promise_test(() => {
+
+  const promises = [];
+  for (const size of [NaN, -Infinity, Infinity, -1]) {
+    let theError;
+    const rs = new ReadableStream(
+      {
+        start(c) {
+          try {
+            c.enqueue('hi');
+            assert_unreached('enqueue didn\'t throw');
+          } catch (error) {
+            assert_equals(error.name, 'RangeError', 'enqueue should throw a RangeError for ' + size);
+            theError = error;
+          }
+        }
+      },
+      {
+        size() {
+          return size;
+        },
+        highWaterMark: 5
+      }
+    );
+
+    promises.push(rs.getReader().closed.catch(e => {
+      assert_equals(e, theError, 'closed should reject with the error for ' + size);
+    }));
+  }
+
+  return Promise.all(promises);
+
+}, 'Readable stream: invalid strategy.size return value');
diff --git a/testing/web-platform/tests/streams/readable-streams/bad-underlying-sources.any.js b/testing/web-platform/tests/streams/readable-streams/bad-underlying-sources.any.js
new file mode 100644
index 0000000000..e9cf4c9249
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/bad-underlying-sources.any.js
@@ -0,0 +1,400 @@
+// META: global=window,worker
+'use strict';
+
+
+test(() => {
+
+  const theError = new Error('a unique string');
+
+  assert_throws_exactly(theError, () => {
+    new ReadableStream({
+      get start() {
+        throw theError;
+      }
+    });
+  }, 'constructing the stream should re-throw the error');
+
+}, 'Underlying source start: throwing getter');
+
+
+test(() => {
+
+  const theError = new Error('a unique string');
+
+  assert_throws_exactly(theError, () => {
+    new ReadableStream({
+      start() {
+        throw theError;
+      }
+    });
+  }, 'constructing the stream should re-throw the error');
+
+}, 'Underlying source start: throwing method');
+
+
+test(() => {
+
+  const theError = new Error('a unique string');
+  assert_throws_exactly(theError, () => new ReadableStream({
+    get pull() {
+      throw theError;
+    }
+  }), 'constructor should throw');
+
+}, 'Underlying source: throwing pull getter (initial pull)');
+
+
+promise_test(t => {
+
+  const theError = new Error('a unique string');
+  const rs = new ReadableStream({
+    pull() {
+      throw theError;
+    }
+  });
+
+  return promise_rejects_exactly(t, theError, rs.getReader().closed);
+
+}, 'Underlying source: throwing pull method (initial pull)');
+
+
+promise_test(t => {
+
+  const theError = new Error('a unique string');
+
+  let counter = 0;
+  const rs = new ReadableStream({
+    get pull() {
+      ++counter;
+      if (counter === 1) {
+        return c => c.enqueue('a');
+      }
+
+      throw theError;
+    }
+  });
+  const reader = rs.getReader();
+
+  return Promise.all([
+    reader.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'the first chunk read should be correct');
+    }),
+    reader.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'the second chunk read should be correct');
+      assert_equals(counter, 1, 'counter should be 1');
+    })
+  ]);
+
+}, 'Underlying source pull: throwing getter (second pull does not result in a second get)');
+
+promise_test(t => {
+
+  const theError = new Error('a unique string');
+
+  let counter = 0;
+  const rs = new ReadableStream({
+    pull(c) {
+      ++counter;
+      if (counter === 1) {
+        c.enqueue('a');
+        return;
+      }
+
+      throw theError;
+    }
+  });
+  const reader = rs.getReader();
+
+  return Promise.all([
+    reader.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'the chunk read should be correct');
+    }),
+    promise_rejects_exactly(t, theError, reader.closed)
+  ]);
+
+}, 'Underlying source pull: throwing method (second pull)');
+
+test(() => {
+
+  const theError = new Error('a unique string');
+  assert_throws_exactly(theError, () => new ReadableStream({
+    get cancel() {
+      throw theError;
+    }
+  }), 'constructor should throw');
+
+}, 'Underlying source cancel: throwing getter');
+
+promise_test(t => {
+
+  const theError = new Error('a unique string');
+  const rs = new ReadableStream({
+    cancel() {
+      throw theError;
+    }
+  });
+
+  return promise_rejects_exactly(t, theError, rs.cancel());
+
+}, 'Underlying source cancel: throwing method');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  rs.cancel();
+  assert_throws_js(TypeError, () => controller.enqueue('a'), 'Calling enqueue after canceling should throw');
+
+  return rs.getReader().closed;
+
+}, 'Underlying source: calling enqueue on an empty canceled stream should throw');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      controller = c;
+    }
+  });
+
+  rs.cancel();
+  assert_throws_js(TypeError, () => controller.enqueue('c'), 'Calling enqueue after canceling should throw');
+
+  return rs.getReader().closed;
+
+}, 'Underlying source: calling enqueue on a non-empty canceled stream should throw');
+
+promise_test(() => {
+
+  return new ReadableStream({
+    start(c) {
+      c.close();
+      assert_throws_js(TypeError, () => c.enqueue('a'), 'call to enqueue should throw a TypeError');
+    }
+  }).getReader().closed;
+
+}, 'Underlying source: calling enqueue on a closed stream should throw');
+
+promise_test(t => {
+
+  const theError = new Error('boo');
+  const closed = new ReadableStream({
+    start(c) {
+      c.error(theError);
+      assert_throws_js(TypeError, () => c.enqueue('a'), 'call to enqueue should throw the error');
+    }
+  }).getReader().closed;
+
+  return promise_rejects_exactly(t, theError, closed);
+
+}, 'Underlying source: calling enqueue on an errored stream should throw');
+
+promise_test(() => {
+
+  return new ReadableStream({
+    start(c) {
+      c.close();
+      assert_throws_js(TypeError, () => c.close(), 'second call to close should throw a TypeError');
+    }
+  }).getReader().closed;
+
+}, 'Underlying source: calling close twice on an empty stream should throw the second time');
+
+promise_test(() => {
+
+  let startCalled = false;
+  let readCalled = false;
+  const reader = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.close();
+      assert_throws_js(TypeError, () => c.close(), 'second call to close should throw a TypeError');
+      startCalled = true;
+    }
+  }).getReader();
+
+  return Promise.all([
+    reader.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'read() should read the enqueued chunk');
+      readCalled = true;
+    }),
+    reader.closed.then(() => {
+      assert_true(startCalled);
+      assert_true(readCalled);
+    })
+  ]);
+
+}, 'Underlying source: calling close twice on a non-empty stream should throw the second time');
+
+promise_test(() => {
+
+  let controller;
+  let startCalled = false;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+      startCalled = true;
+    }
+  });
+
+  rs.cancel();
+  assert_throws_js(TypeError, () => controller.close(), 'Calling close after canceling should throw');
+
+  return rs.getReader().closed.then(() => {
+    assert_true(startCalled);
+  });
+
+}, 'Underlying source: calling close on an empty canceled stream should throw');
+
+promise_test(() => {
+
+  let controller;
+  let startCalled = false;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+      c.enqueue('a');
+      startCalled = true;
+    }
+  });
+
+  rs.cancel();
+  assert_throws_js(TypeError, () => controller.close(), 'Calling close after canceling should throw');
+
+  return rs.getReader().closed.then(() => {
+    assert_true(startCalled);
+  });
+
+}, 'Underlying source: calling close on a non-empty canceled stream should throw');
+
+promise_test(() => {
+
+  const theError = new Error('boo');
+  let startCalled = false;
+
+  const closed = new ReadableStream({
+    start(c) {
+      c.error(theError);
+      assert_throws_js(TypeError, () => c.close(), 'call to close should throw a TypeError');
+      startCalled = true;
+    }
+  }).getReader().closed;
+
+  return closed.catch(e => {
+    assert_true(startCalled);
+    assert_equals(e, theError, 'closed should reject with the error');
+  });
+
+}, 'Underlying source: calling close after error should throw');
+
+promise_test(() => {
+
+  const theError = new Error('boo');
+  let startCalled = false;
+
+  const closed = new ReadableStream({
+    start(c) {
+      c.error(theError);
+      c.error();
+      startCalled = true;
+    }
+  }).getReader().closed;
+
+  return closed.catch(e => {
+    assert_true(startCalled);
+    assert_equals(e, theError, 'closed should reject with the error');
+  });
+
+}, 'Underlying source: calling error twice should not throw');
+
+promise_test(() => {
+
+  let startCalled = false;
+
+  const closed = new ReadableStream({
+    start(c) {
+      c.close();
+      c.error();
+      startCalled = true;
+    }
+  }).getReader().closed;
+
+  return closed.then(() => assert_true(startCalled));
+
+}, 'Underlying source: calling error after close should not throw');
+
+promise_test(() => {
+
+  let startCalled = false;
+  const firstError = new Error('1');
+  const secondError = new Error('2');
+
+  const closed = new ReadableStream({
+    start(c) {
+      c.error(firstError);
+      startCalled = true;
+      return Promise.reject(secondError);
+    }
+  }).getReader().closed;
+
+  return closed.catch(e => {
+    assert_true(startCalled);
+    assert_equals(e, firstError, 'closed should reject with the first error');
+  });
+
+}, 'Underlying source: calling error and returning a rejected promise from start should cause the stream to error ' +
+   'with the first error');
+
+promise_test(() => {
+
+  let startCalled = false;
+  const firstError = new Error('1');
+  const secondError = new Error('2');
+
+  const closed = new ReadableStream({
+    pull(c) {
+      c.error(firstError);
+      startCalled = true;
+      return Promise.reject(secondError);
+    }
+  }).getReader().closed;
+
+  return closed.catch(e => {
+    assert_true(startCalled);
+    assert_equals(e, firstError, 'closed should reject with the first error');
+  });
+
+}, 'Underlying source: calling error and returning a rejected promise from pull should cause the stream to error ' +
+   'with the first error');
+
+const error1 = { name: 'error1' };
+
+promise_test(t => {
+
+  let pullShouldThrow = false;
+  const rs = new ReadableStream({
+    pull(controller) {
+      if (pullShouldThrow) {
+        throw error1;
+      }
+      controller.enqueue(0);
+    }
+  }, new CountQueuingStrategy({highWaterMark: 1}));
+  const reader = rs.getReader();
+  return Promise.resolve().then(() => {
+    pullShouldThrow = true;
+    return Promise.all([
+      reader.read(),
+      promise_rejects_exactly(t, error1, reader.closed, '.closed promise should reject')
+    ]);
+  });
+
+}, 'read should not error if it dequeues and pull() throws');
diff --git a/testing/web-platform/tests/streams/readable-streams/cancel.any.js b/testing/web-platform/tests/streams/readable-streams/cancel.any.js
new file mode 100644
index 0000000000..800bd99441
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/cancel.any.js
@@ -0,0 +1,236 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+'use strict';
+
+promise_test(t => {
+
+  const randomSource = new RandomPushSource();
+
+  let cancellationFinished = false;
+  const rs = new ReadableStream({
+    start(c) {
+      randomSource.ondata = c.enqueue.bind(c);
+      randomSource.onend = c.close.bind(c);
+      randomSource.onerror = c.error.bind(c);
+    },
+
+    pull() {
+      randomSource.readStart();
+    },
+
+    cancel() {
+      randomSource.readStop();
+
+      return new Promise(resolve => {
+        t.step_timeout(() => {
+          cancellationFinished = true;
+          resolve();
+        }, 1);
+      });
+    }
+  });
+
+  const reader = rs.getReader();
+
+  // We call delay multiple times to avoid cancelling too early for the
+  // source to enqueue at least one chunk.
+  const cancel = delay(5).then(() => delay(5)).then(() => delay(5)).then(() => {
+    const cancelPromise = reader.cancel();
+    assert_false(cancellationFinished, 'cancellation in source should happen later');
+    return cancelPromise;
+  });
+
+  return readableStreamToArray(rs, reader).then(chunks => {
+    assert_greater_than(chunks.length, 0, 'at least one chunk should be read');
+    for (let i = 0; i < chunks.length; i++) {
+      assert_equals(chunks[i].length, 128, 'chunk ' + i + ' should have 128 bytes');
+    }
+    return cancel;
+  }).then(() => {
+    assert_true(cancellationFinished, 'it returns a promise that is fulfilled when the cancellation finishes');
+  });
+
+}, 'ReadableStream cancellation: integration test on an infinite stream derived from a random push source');
+
+test(() => {
+
+  let recordedReason;
+  const rs = new ReadableStream({
+    cancel(reason) {
+      recordedReason = reason;
+    }
+  });
+
+  const passedReason = new Error('Sorry, it just wasn\'t meant to be.');
+  rs.cancel(passedReason);
+
+  assert_equals(recordedReason, passedReason,
+    'the error passed to the underlying source\'s cancel method should equal the one passed to the stream\'s cancel');
+
+}, 'ReadableStream cancellation: cancel(reason) should pass through the given reason to the underlying source');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.close();
+    },
+    cancel() {
+      assert_unreached('underlying source cancel() should not have been called');
+    }
+  });
+
+  const reader = rs.getReader();
+
+  return rs.cancel().then(() => {
+    assert_unreached('cancel() should be rejected');
+  }, e => {
+    assert_equals(e.name, 'TypeError', 'cancel() should be rejected with a TypeError');
+  }).then(() => {
+    return reader.read();
+  }).then(result => {
+    assert_object_equals(result, { value: 'a', done: false }, 'read() should still work after the attempted cancel');
+    return reader.closed;
+  });
+
+}, 'ReadableStream cancellation: cancel() on a locked stream should fail and not call the underlying source cancel');
+
+promise_test(() => {
+
+  let cancelReceived = false;
+  const cancelReason = new Error('I am tired of this stream, I prefer to cancel it');
+  const rs = new ReadableStream({
+    cancel(reason) {
+      cancelReceived = true;
+      assert_equals(reason, cancelReason, 'cancellation reason given to the underlying source should be equal to the one passed');
+    }
+  });
+
+  return rs.cancel(cancelReason).then(() => {
+    assert_true(cancelReceived);
+  });
+
+}, 'ReadableStream cancellation: should fulfill promise when cancel callback went fine');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    cancel() {
+      return 'Hello';
+    }
+  });
+
+  return rs.cancel().then(v => {
+    assert_equals(v, undefined, 'cancel() return value should be fulfilled with undefined');
+  });
+
+}, 'ReadableStream cancellation: returning a value from the underlying source\'s cancel should not affect the fulfillment value of the promise returned by the stream\'s cancel');
+
+promise_test(() => {
+
+  const thrownError = new Error('test');
+  let cancelCalled = false;
+
+  const rs = new ReadableStream({
+    cancel() {
+      cancelCalled = true;
+      throw thrownError;
+    }
+  });
+
+  return rs.cancel('test').then(() => {
+    assert_unreached('cancel should reject');
+  }, e => {
+    assert_true(cancelCalled);
+    assert_equals(e, thrownError);
+  });
+
+}, 'ReadableStream cancellation: should reject promise when cancel callback raises an exception');
+
+promise_test(() => {
+
+  const cancelReason = new Error('test');
+
+  const rs = new ReadableStream({
+    cancel(error) {
+      assert_equals(error, cancelReason);
+      return delay(1);
+    }
+  });
+
+  return rs.cancel(cancelReason);
+
+}, 'ReadableStream cancellation: if the underlying source\'s cancel method returns a promise, the promise returned by the stream\'s cancel should fulfill when that one does (1)');
+
+promise_test(t => {
+
+  let resolveSourceCancelPromise;
+  let sourceCancelPromiseHasFulfilled = false;
+
+  const rs = new ReadableStream({
+    cancel() {
+      const sourceCancelPromise = new Promise(resolve => resolveSourceCancelPromise = resolve);
+
+      sourceCancelPromise.then(() => {
+        sourceCancelPromiseHasFulfilled = true;
+      });
+
+      return sourceCancelPromise;
+    }
+  });
+
+  t.step_timeout(() => resolveSourceCancelPromise('Hello'), 1);
+
+  return rs.cancel().then(value => {
+    assert_true(sourceCancelPromiseHasFulfilled, 'cancel() return value should be fulfilled only after the promise returned by the underlying source\'s cancel');
+    assert_equals(value, undefined, 'cancel() return value should be fulfilled with undefined');
+  });
+
+}, 'ReadableStream cancellation: if the underlying source\'s cancel method returns a promise, the promise returned by the stream\'s cancel should fulfill when that one does (2)');
+
+promise_test(t => {
+
+  let rejectSourceCancelPromise;
+  let sourceCancelPromiseHasRejected = false;
+
+  const rs = new ReadableStream({
+    cancel() {
+      const sourceCancelPromise = new Promise((resolve, reject) => rejectSourceCancelPromise = reject);
+
+      sourceCancelPromise.catch(() => {
+        sourceCancelPromiseHasRejected = true;
+      });
+
+      return sourceCancelPromise;
+    }
+  });
+
+  const errorInCancel = new Error('Sorry, it just wasn\'t meant to be.');
+
+  t.step_timeout(() => rejectSourceCancelPromise(errorInCancel), 1);
+
+  return rs.cancel().then(() => {
+    assert_unreached('cancel() return value should be rejected');
+  }, r => {
+    assert_true(sourceCancelPromiseHasRejected, 'cancel() return value should be rejected only after the promise returned by the underlying source\'s cancel');
+    assert_equals(r, errorInCancel, 'cancel() return value should be rejected with the underlying source\'s rejection reason');
+  });
+
+}, 'ReadableStream cancellation: if the underlying source\'s cancel method returns a promise, the promise returned by the stream\'s cancel should reject when that one does');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start() {
+      return new Promise(() => {});
+    },
+    pull() {
+      assert_unreached('pull should not have been called');
+    }
+  });
+
+  return Promise.all([rs.cancel(), rs.getReader().closed]);
+
+}, 'ReadableStream cancellation: cancelling before start finishes should prevent pull() from being called');
diff --git a/testing/web-platform/tests/streams/readable-streams/constructor.any.js b/testing/web-platform/tests/streams/readable-streams/constructor.any.js
new file mode 100644
index 0000000000..608dc48cfa
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/constructor.any.js
@@ -0,0 +1,17 @@
+// META: global=window,worker
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+test(() => {
+  const underlyingSource = { get start() { throw error1; } };
+  const queuingStrategy = { highWaterMark: 0, get size() { throw error2; } };
+
+  // underlyingSource is converted in prose in the method body, whereas queuingStrategy is done at the IDL layer.
+  // So the queuingStrategy exception should be encountered first.
+  assert_throws_exactly(error2, () => new ReadableStream(underlyingSource, queuingStrategy));
+}, 'underlyingSource argument should be converted after queuingStrategy argument');
diff --git a/testing/web-platform/tests/streams/readable-streams/count-queuing-strategy-integration.any.js b/testing/web-platform/tests/streams/readable-streams/count-queuing-strategy-integration.any.js
new file mode 100644
index 0000000000..02ac5bae5c
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/count-queuing-strategy-integration.any.js
@@ -0,0 +1,208 @@
+// META: global=window,worker
+'use strict';
+
+test(() => {
+
+  new ReadableStream({}, new CountQueuingStrategy({ highWaterMark: 4 }));
+
+}, 'Can construct a readable stream with a valid CountQueuingStrategy');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        controller = c;
+      }
+    },
+    new CountQueuingStrategy({ highWaterMark: 0 })
+  );
+  const reader = rs.getReader();
+
+  assert_equals(controller.desiredSize, 0, '0 reads, 0 enqueues: desiredSize should be 0');
+  controller.enqueue('a');
+  assert_equals(controller.desiredSize, -1, '0 reads, 1 enqueue: desiredSize should be -1');
+  controller.enqueue('b');
+  assert_equals(controller.desiredSize, -2, '0 reads, 2 enqueues: desiredSize should be -2');
+  controller.enqueue('c');
+  assert_equals(controller.desiredSize, -3, '0 reads, 3 enqueues: desiredSize should be -3');
+  controller.enqueue('d');
+  assert_equals(controller.desiredSize, -4, '0 reads, 4 enqueues: desiredSize should be -4');
+
+  return reader.read()
+    .then(result => {
+      assert_object_equals(result, { value: 'a', done: false },
+                           '1st read gives back the 1st chunk enqueued (queue now contains 3 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'b', done: false },
+                           '2nd read gives back the 2nd chunk enqueued (queue now contains 2 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'c', done: false },
+                           '3rd read gives back the 3rd chunk enqueued (queue now contains 1 chunk)');
+
+      assert_equals(controller.desiredSize, -1, '3 reads, 4 enqueues: desiredSize should be -1');
+      controller.enqueue('e');
+      assert_equals(controller.desiredSize, -2, '3 reads, 5 enqueues: desiredSize should be -2');
+
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'd', done: false },
+                           '4th read gives back the 4th chunk enqueued (queue now contains 1 chunks)');
+      return reader.read();
+
+    }).then(result => {
+      assert_object_equals(result, { value: 'e', done: false },
+                           '5th read gives back the 5th chunk enqueued (queue now contains 0 chunks)');
+
+      assert_equals(controller.desiredSize, 0, '5 reads, 5 enqueues: desiredSize should be 0');
+      controller.enqueue('f');
+      assert_equals(controller.desiredSize, -1, '5 reads, 6 enqueues: desiredSize should be -1');
+      controller.enqueue('g');
+      assert_equals(controller.desiredSize, -2, '5 reads, 7 enqueues: desiredSize should be -2');
+    });
+
+}, 'Correctly governs a ReadableStreamController\'s desiredSize property (HWM = 0)');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        controller = c;
+      }
+    },
+    new CountQueuingStrategy({ highWaterMark: 1 })
+  );
+  const reader = rs.getReader();
+
+  assert_equals(controller.desiredSize, 1, '0 reads, 0 enqueues: desiredSize should be 1');
+  controller.enqueue('a');
+  assert_equals(controller.desiredSize, 0, '0 reads, 1 enqueue: desiredSize should be 0');
+  controller.enqueue('b');
+  assert_equals(controller.desiredSize, -1, '0 reads, 2 enqueues: desiredSize should be -1');
+  controller.enqueue('c');
+  assert_equals(controller.desiredSize, -2, '0 reads, 3 enqueues: desiredSize should be -2');
+  controller.enqueue('d');
+  assert_equals(controller.desiredSize, -3, '0 reads, 4 enqueues: desiredSize should be -3');
+
+  return reader.read()
+    .then(result => {
+      assert_object_equals(result, { value: 'a', done: false },
+                           '1st read gives back the 1st chunk enqueued (queue now contains 3 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'b', done: false },
+                           '2nd read gives back the 2nd chunk enqueued (queue now contains 2 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'c', done: false },
+                           '3rd read gives back the 3rd chunk enqueued (queue now contains 1 chunk)');
+
+      assert_equals(controller.desiredSize, 0, '3 reads, 4 enqueues: desiredSize should be 0');
+      controller.enqueue('e');
+      assert_equals(controller.desiredSize, -1, '3 reads, 5 enqueues: desiredSize should be -1');
+
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'd', done: false },
+                           '4th read gives back the 4th chunk enqueued (queue now contains 1 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'e', done: false },
+                           '5th read gives back the 5th chunk enqueued (queue now contains 0 chunks)');
+
+      assert_equals(controller.desiredSize, 1, '5 reads, 5 enqueues: desiredSize should be 1');
+      controller.enqueue('f');
+      assert_equals(controller.desiredSize, 0, '5 reads, 6 enqueues: desiredSize should be 0');
+      controller.enqueue('g');
+      assert_equals(controller.desiredSize, -1, '5 reads, 7 enqueues: desiredSize should be -1');
+    });
+
+}, 'Correctly governs a ReadableStreamController\'s desiredSize property (HWM = 1)');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        controller = c;
+      }
+    },
+    new CountQueuingStrategy({ highWaterMark: 4 })
+  );
+  const reader = rs.getReader();
+
+  assert_equals(controller.desiredSize, 4, '0 reads, 0 enqueues: desiredSize should be 4');
+  controller.enqueue('a');
+  assert_equals(controller.desiredSize, 3, '0 reads, 1 enqueue: desiredSize should be 3');
+  controller.enqueue('b');
+  assert_equals(controller.desiredSize, 2, '0 reads, 2 enqueues: desiredSize should be 2');
+  controller.enqueue('c');
+  assert_equals(controller.desiredSize, 1, '0 reads, 3 enqueues: desiredSize should be 1');
+  controller.enqueue('d');
+  assert_equals(controller.desiredSize, 0, '0 reads, 4 enqueues: desiredSize should be 0');
+  controller.enqueue('e');
+  assert_equals(controller.desiredSize, -1, '0 reads, 5 enqueues: desiredSize should be -1');
+  controller.enqueue('f');
+  assert_equals(controller.desiredSize, -2, '0 reads, 6 enqueues: desiredSize should be -2');
+
+
+  return reader.read()
+    .then(result => {
+      assert_object_equals(result, { value: 'a', done: false },
+                           '1st read gives back the 1st chunk enqueued (queue now contains 5 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'b', done: false },
+                           '2nd read gives back the 2nd chunk enqueued (queue now contains 4 chunks)');
+
+      assert_equals(controller.desiredSize, 0, '2 reads, 6 enqueues: desiredSize should be 0');
+      controller.enqueue('g');
+      assert_equals(controller.desiredSize, -1, '2 reads, 7 enqueues: desiredSize should be -1');
+
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'c', done: false },
+                           '3rd read gives back the 3rd chunk enqueued (queue now contains 4 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'd', done: false },
+                           '4th read gives back the 4th chunk enqueued (queue now contains 3 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'e', done: false },
+                           '5th read gives back the 5th chunk enqueued (queue now contains 2 chunks)');
+      return reader.read();
+    })
+    .then(result => {
+      assert_object_equals(result, { value: 'f', done: false },
+                           '6th read gives back the 6th chunk enqueued (queue now contains 0 chunks)');
+
+      assert_equals(controller.desiredSize, 3, '6 reads, 7 enqueues: desiredSize should be 3');
+      controller.enqueue('h');
+      assert_equals(controller.desiredSize, 2, '6 reads, 8 enqueues: desiredSize should be 2');
+      controller.enqueue('i');
+      assert_equals(controller.desiredSize, 1, '6 reads, 9 enqueues: desiredSize should be 1');
+      controller.enqueue('j');
+      assert_equals(controller.desiredSize, 0, '6 reads, 10 enqueues: desiredSize should be 0');
+      controller.enqueue('k');
+      assert_equals(controller.desiredSize, -1, '6 reads, 11 enqueues: desiredSize should be -1');
+    });
+
+}, 'Correctly governs a ReadableStreamController\'s desiredSize property (HWM = 4)');
diff --git a/testing/web-platform/tests/streams/readable-streams/crashtests/empty.js b/testing/web-platform/tests/streams/readable-streams/crashtests/empty.js
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/crashtests/empty.js
diff --git a/testing/web-platform/tests/streams/readable-streams/crashtests/strategy-worker-terminate.html b/testing/web-platform/tests/streams/readable-streams/crashtests/strategy-worker-terminate.html
new file mode 100644
index 0000000000..a75c3c66b6
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/crashtests/strategy-worker-terminate.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html class="test-wait">
+<meta charset="utf-8">
+<script>
+  var c = new Worker("/streams/readable-streams/crashtests/strategy-worker.js");
+  c.onmessage = () => {
+    c.terminate();
+    document.documentElement.classList.remove("test-wait");
+  }
+</script>
diff --git a/testing/web-platform/tests/streams/readable-streams/crashtests/strategy-worker.js b/testing/web-platform/tests/streams/readable-streams/crashtests/strategy-worker.js
new file mode 100644
index 0000000000..dd0ab03b55
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/crashtests/strategy-worker.js
@@ -0,0 +1,4 @@
+var b = new CountQueuingStrategy({ highWaterMark: 3 });
+
+importScripts("empty.js");
+postMessage("done");
diff --git a/testing/web-platform/tests/streams/readable-streams/cross-realm-crash.window.js b/testing/web-platform/tests/streams/readable-streams/cross-realm-crash.window.js
new file mode 100644
index 0000000000..5fc7ce37a5
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/cross-realm-crash.window.js
@@ -0,0 +1,13 @@
+// This is a repro for a crash bug that existed in Blink. See
+// https://crbug.com/1290014. If there's no crash then the test passed.
+
+test(t => {
+  const iframeTag = document.createElement('iframe');
+  document.body.appendChild(iframeTag);
+
+  const readableStream = new ReadableStream();
+  const reader = new iframeTag.contentWindow.ReadableStreamDefaultReader(readableStream);
+  iframeTag.remove();
+  reader.cancel();
+  reader.read();
+}, 'should not crash on reading from stream cancelled in destroyed realm');
diff --git a/testing/web-platform/tests/streams/readable-streams/default-reader.any.js b/testing/web-platform/tests/streams/readable-streams/default-reader.any.js
new file mode 100644
index 0000000000..59d7ab2f74
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/default-reader.any.js
@@ -0,0 +1,539 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+'use strict';
+
+test(() => {
+
+  assert_throws_js(TypeError, () => new ReadableStreamDefaultReader('potato'));
+  assert_throws_js(TypeError, () => new ReadableStreamDefaultReader({}));
+  assert_throws_js(TypeError, () => new ReadableStreamDefaultReader());
+
+}, 'ReadableStreamDefaultReader constructor should get a ReadableStream object as argument');
+
+test(() => {
+
+  const rsReader = new ReadableStreamDefaultReader(new ReadableStream());
+  assert_equals(rsReader.closed, rsReader.closed, 'closed should return the same promise');
+
+}, 'ReadableStreamDefaultReader closed should always return the same promise object');
+
+test(() => {
+
+  const rs = new ReadableStream();
+  new ReadableStreamDefaultReader(rs); // Constructing directly the first time should be fine.
+  assert_throws_js(TypeError, () => new ReadableStreamDefaultReader(rs),
+                   'constructing directly the second time should fail');
+
+}, 'Constructing a ReadableStreamDefaultReader directly should fail if the stream is already locked (via direct ' +
+   'construction)');
+
+test(() => {
+
+  const rs = new ReadableStream();
+  new ReadableStreamDefaultReader(rs); // Constructing directly should be fine.
+  assert_throws_js(TypeError, () => rs.getReader(), 'getReader() should fail');
+
+}, 'Getting a ReadableStreamDefaultReader via getReader should fail if the stream is already locked (via direct ' +
+   'construction)');
+
+test(() => {
+
+  const rs = new ReadableStream();
+  rs.getReader(); // getReader() should be fine.
+  assert_throws_js(TypeError, () => new ReadableStreamDefaultReader(rs), 'constructing directly should fail');
+
+}, 'Constructing a ReadableStreamDefaultReader directly should fail if the stream is already locked (via getReader)');
+
+test(() => {
+
+  const rs = new ReadableStream();
+  rs.getReader(); // getReader() should be fine.
+  assert_throws_js(TypeError, () => rs.getReader(), 'getReader() should fail');
+
+}, 'Getting a ReadableStreamDefaultReader via getReader should fail if the stream is already locked (via getReader)');
+
+test(() => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+
+  new ReadableStreamDefaultReader(rs); // Constructing directly should not throw.
+
+}, 'Constructing a ReadableStreamDefaultReader directly should be OK if the stream is closed');
+
+test(() => {
+
+  const theError = new Error('don\'t say i didn\'t warn ya');
+  const rs = new ReadableStream({
+    start(c) {
+      c.error(theError);
+    }
+  });
+
+  new ReadableStreamDefaultReader(rs); // Constructing directly should not throw.
+
+}, 'Constructing a ReadableStreamDefaultReader directly should be OK if the stream is errored');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const reader = rs.getReader();
+
+  const promise = reader.read().then(result => {
+    assert_object_equals(result, { value: 'a', done: false }, 'read() should fulfill with the enqueued chunk');
+  });
+
+  controller.enqueue('a');
+  return promise;
+
+}, 'Reading from a reader for an empty stream will wait until a chunk is available');
+
+promise_test(() => {
+
+  let cancelCalled = false;
+  const passedReason = new Error('it wasn\'t the right time, sorry');
+  const rs = new ReadableStream({
+    cancel(reason) {
+      assert_true(rs.locked, 'the stream should still be locked');
+      assert_throws_js(TypeError, () => rs.getReader(), 'should not be able to get another reader');
+      assert_equals(reason, passedReason, 'the cancellation reason is passed through to the underlying source');
+      cancelCalled = true;
+    }
+  });
+
+  const reader = rs.getReader();
+  return reader.cancel(passedReason).then(() => assert_true(cancelCalled));
+
+}, 'cancel() on a reader does not release the reader');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const reader = rs.getReader();
+  const promise = reader.closed;
+
+  controller.close();
+  return promise;
+
+}, 'closed should be fulfilled after stream is closed (.closed access before acquiring)');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const reader1 = rs.getReader();
+
+  reader1.releaseLock();
+
+  const reader2 = rs.getReader();
+  controller.close();
+
+  return Promise.all([
+    promise_rejects_js(t, TypeError, reader1.closed),
+    reader2.closed
+  ]);
+
+}, 'closed should be rejected after reader releases its lock (multiple stream locks)');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const reader = rs.getReader();
+  const promise1 = reader.closed;
+
+  controller.close();
+
+  reader.releaseLock();
+  const promise2 = reader.closed;
+
+  assert_not_equals(promise1, promise2, '.closed should be replaced');
+  return Promise.all([
+    promise1,
+    promise_rejects_js(t, TypeError, promise2, '.closed after releasing lock'),
+  ]);
+
+}, 'closed is replaced when stream closes and reader releases its lock');
+
+promise_test(t => {
+
+  const theError = { name: 'unique error' };
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const reader = rs.getReader();
+  const promise1 = reader.closed;
+
+  controller.error(theError);
+
+  reader.releaseLock();
+  const promise2 = reader.closed;
+
+  assert_not_equals(promise1, promise2, '.closed should be replaced');
+  return Promise.all([
+    promise_rejects_exactly(t, theError, promise1, '.closed before releasing lock'),
+    promise_rejects_js(t, TypeError, promise2, '.closed after releasing lock')
+  ]);
+
+}, 'closed is replaced when stream errors and reader releases its lock');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.close();
+    }
+  });
+
+  const reader1 = rs.getReader();
+  const promise1 = reader1.read().then(r => {
+    assert_object_equals(r, { value: 'a', done: false }, 'reading the first chunk from reader1 works');
+  });
+  reader1.releaseLock();
+
+  const reader2 = rs.getReader();
+  const promise2 = reader2.read().then(r => {
+    assert_object_equals(r, { value: 'b', done: false }, 'reading the second chunk from reader2 works');
+  });
+  reader2.releaseLock();
+
+  return Promise.all([promise1, promise2]);
+
+}, 'Multiple readers can access the stream in sequence');
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+    }
+  });
+
+  const reader1 = rs.getReader();
+  reader1.releaseLock();
+
+  const reader2 = rs.getReader();
+
+  // Should be a no-op
+  reader1.releaseLock();
+
+  return reader2.read().then(result => {
+    assert_object_equals(result, { value: 'a', done: false },
+                         'read() should still work on reader2 even after reader1 is released');
+  });
+
+}, 'Cannot use an already-released reader to unlock a stream again');
+
+promise_test(t => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+    },
+    cancel() {
+      assert_unreached('underlying source cancel should not be called');
+    }
+  });
+
+  const reader = rs.getReader();
+  reader.releaseLock();
+  const cancelPromise = reader.cancel();
+
+  const reader2 = rs.getReader();
+  const readPromise = reader2.read().then(r => {
+    assert_object_equals(r, { value: 'a', done: false }, 'a new reader should be able to read a chunk');
+  });
+
+  return Promise.all([
+    promise_rejects_js(t, TypeError, cancelPromise),
+    readPromise
+  ]);
+
+}, 'cancel() on a released reader is a no-op and does not pass through');
+
+promise_test(t => {
+
+  const promiseAsserts = [];
+
+  let controller;
+  const theError = { name: 'unique error' };
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const reader1 = rs.getReader();
+
+  promiseAsserts.push(
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader1.read())
+  );
+
+  assert_throws_js(TypeError, () => rs.getReader(), 'trying to get another reader before erroring should throw');
+
+  controller.error(theError);
+
+  reader1.releaseLock();
+
+  const reader2 = rs.getReader();
+
+  promiseAsserts.push(
+    promise_rejects_exactly(t, theError, reader2.closed),
+    promise_rejects_exactly(t, theError, reader2.read())
+  );
+
+  return Promise.all(promiseAsserts);
+
+}, 'Getting a second reader after erroring the stream and releasing the reader should succeed');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const promise = rs.getReader().closed.then(
+    t.unreached_func('closed promise should not be fulfilled when stream is errored'),
+    err => {
+      assert_equals(err, undefined, 'passed error should be undefined as it was');
+    }
+  );
+
+  controller.error();
+  return promise;
+
+}, 'ReadableStreamDefaultReader closed promise should be rejected with undefined if that is the error');
+
+
+promise_test(t => {
+
+  const rs = new ReadableStream({
+    start() {
+      return Promise.reject();
+    }
+  });
+
+  return rs.getReader().read().then(
+    t.unreached_func('read promise should not be fulfilled when stream is errored'),
+    err => {
+      assert_equals(err, undefined, 'passed error should be undefined as it was');
+    }
+  );
+
+}, 'ReadableStreamDefaultReader: if start rejects with no parameter, it should error the stream with an undefined ' +
+    'error');
+
+promise_test(t => {
+
+  const theError = { name: 'unique string' };
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const promise = promise_rejects_exactly(t, theError, rs.getReader().closed);
+
+  controller.error(theError);
+  return promise;
+
+}, 'Erroring a ReadableStream after checking closed should reject ReadableStreamDefaultReader closed promise');
+
+promise_test(t => {
+
+  const theError = { name: 'unique string' };
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  controller.error(theError);
+
+  // Let's call getReader twice for extra test coverage of this code path.
+  rs.getReader().releaseLock();
+
+  return promise_rejects_exactly(t, theError, rs.getReader().closed);
+
+}, 'Erroring a ReadableStream before checking closed should reject ReadableStreamDefaultReader closed promise');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const reader = rs.getReader();
+
+  const promise = Promise.all([
+    reader.read().then(result => {
+      assert_object_equals(result, { value: undefined, done: true }, 'read() should fulfill with close (1)');
+    }),
+    reader.read().then(result => {
+      assert_object_equals(result, { value: undefined, done: true }, 'read() should fulfill with close (2)');
+    }),
+    reader.closed
+  ]);
+
+  controller.close();
+  return promise;
+
+}, 'Reading twice on a stream that gets closed');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  controller.close();
+  const reader = rs.getReader();
+
+  return Promise.all([
+    reader.read().then(result => {
+      assert_object_equals(result, { value: undefined, done: true }, 'read() should fulfill with close (1)');
+    }),
+    reader.read().then(result => {
+      assert_object_equals(result, { value: undefined, done: true }, 'read() should fulfill with close (2)');
+    }),
+    reader.closed
+  ]);
+
+}, 'Reading twice on a closed stream');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const myError = { name: 'mashed potatoes' };
+  controller.error(myError);
+
+  const reader = rs.getReader();
+
+  return Promise.all([
+    promise_rejects_exactly(t, myError, reader.read()),
+    promise_rejects_exactly(t, myError, reader.read()),
+    promise_rejects_exactly(t, myError, reader.closed)
+  ]);
+
+}, 'Reading twice on an errored stream');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const myError = { name: 'mashed potatoes' };
+  const reader = rs.getReader();
+
+  const promise = Promise.all([
+    promise_rejects_exactly(t, myError, reader.read()),
+    promise_rejects_exactly(t, myError, reader.read()),
+    promise_rejects_exactly(t, myError, reader.closed)
+  ]);
+
+  controller.error(myError);
+  return promise;
+
+}, 'Reading twice on a stream that gets errored');
+
+test(() => {
+  const rs = new ReadableStream();
+  let toStringCalled = false;
+  const mode = {
+    toString() {
+      toStringCalled = true;
+      return '';
+    }
+  };
+  assert_throws_js(TypeError, () => rs.getReader({ mode }), 'getReader() should throw');
+  assert_true(toStringCalled, 'toString() should be called');
+}, 'getReader() should call ToString() on mode');
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.close();
+    }
+  });
+
+  const reader = rs.getReader();
+  return reader.read().then(() => {
+    // The test passes if releaseLock() does not throw.
+    reader.releaseLock();
+  });
+}, 'controller.close() should clear the list of pending read requests');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const reader1 = rs.getReader();
+  const promise1 = promise_rejects_js(t, TypeError, reader1.read(), 'read() from reader1 should reject when reader1 is released');
+  reader1.releaseLock();
+
+  controller.enqueue('a');
+
+  const reader2 = rs.getReader();
+  const promise2 = reader2.read().then(r => {
+    assert_object_equals(r, { value: 'a', done: false }, 'read() from reader2 should resolve with enqueued chunk');
+  })
+  reader2.releaseLock();
+
+  return Promise.all([promise1, promise2]);
+
+}, 'Second reader can read chunks after first reader was released with pending read requests');
diff --git a/testing/web-platform/tests/streams/readable-streams/floating-point-total-queue-size.any.js b/testing/web-platform/tests/streams/readable-streams/floating-point-total-queue-size.any.js
new file mode 100644
index 0000000000..50cca3d951
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/floating-point-total-queue-size.any.js
@@ -0,0 +1,116 @@
+// META: global=window,worker
+'use strict';
+
+// Due to the limitations of floating-point precision, the calculation of desiredSize sometimes gives different answers
+// than adding up the items in the queue would. It is important that implementations give the same result in these edge
+// cases so that developers do not come to depend on non-standard behaviour. See
+// https://github.com/whatwg/streams/issues/582 and linked issues for further discussion.
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(2);
+  assert_equals(controller.desiredSize, 0 - 2, 'desiredSize must be -2 after enqueueing such a chunk');
+
+  controller.enqueue(Number.MAX_SAFE_INTEGER);
+  assert_equals(controller.desiredSize, 0 - Number.MAX_SAFE_INTEGER - 2,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - Number.MAX_SAFE_INTEGER - 2 + 2,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near NUMBER.MAX_SAFE_INTEGER (total ends up positive)');
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(1e-16);
+  assert_equals(controller.desiredSize, 0 - 1e-16, 'desiredSize must be -1e16 after enqueueing such a chunk');
+
+  controller.enqueue(1);
+  assert_equals(controller.desiredSize, 0 - 1e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 + 1e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, but clamped)');
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(1e-16);
+  assert_equals(controller.desiredSize, 0 - 1e-16, 'desiredSize must be -2e16 after enqueueing such a chunk');
+
+  controller.enqueue(1);
+  assert_equals(controller.desiredSize, 0 - 1e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  controller.enqueue(2e-16);
+  assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a third chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16 + 1,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a second chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16 + 1 + 2e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a third chunk)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, and not clamped)');
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(2e-16);
+  assert_equals(controller.desiredSize, 0 - 2e-16, 'desiredSize must be -2e16 after enqueueing such a chunk');
+
+  controller.enqueue(1);
+  assert_equals(controller.desiredSize, 0 - 2e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - 2e-16 - 1 + 2e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a second chunk)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up zero)');
+
+function setupTestStream() {
+  const strategy = {
+    size(x) {
+      return x;
+    },
+    highWaterMark: 0
+  };
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, strategy);
+
+  return { reader: rs.getReader(), controller };
+}
diff --git a/testing/web-platform/tests/streams/readable-streams/garbage-collection.any.js b/testing/web-platform/tests/streams/readable-streams/garbage-collection.any.js
new file mode 100644
index 0000000000..e578176777
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/garbage-collection.any.js
@@ -0,0 +1,71 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=/common/gc.js
+'use strict';
+
+promise_test(async () => {
+
+  let controller;
+  new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  await garbageCollect();
+
+  return delay(50).then(() => {
+    controller.close();
+    assert_throws_js(TypeError, () => controller.close(), 'close should throw a TypeError the second time');
+    controller.error();
+  });
+
+}, 'ReadableStreamController methods should continue working properly when scripts lose their reference to the ' +
+   'readable stream');
+
+promise_test(async () => {
+
+  let controller;
+
+  const closedPromise = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }).getReader().closed;
+
+  await garbageCollect();
+
+  return delay(50).then(() => controller.close()).then(() => closedPromise);
+
+}, 'ReadableStream closed promise should fulfill even if the stream and reader JS references are lost');
+
+promise_test(async t => {
+
+  const theError = new Error('boo');
+  let controller;
+
+  const closedPromise = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }).getReader().closed;
+
+  await garbageCollect();
+
+  return delay(50).then(() => controller.error(theError))
+                  .then(() => promise_rejects_exactly(t, theError, closedPromise));
+
+}, 'ReadableStream closed promise should reject even if stream and reader JS references are lost');
+
+promise_test(async () => {
+
+  const rs = new ReadableStream({});
+
+  rs.getReader();
+
+  await garbageCollect();
+
+  return delay(50).then(() => assert_throws_js(TypeError, () => rs.getReader(),
+    'old reader should still be locking the stream even after garbage collection'));
+
+}, 'Garbage-collecting a ReadableStreamDefaultReader should not unlock its stream');
diff --git a/testing/web-platform/tests/streams/readable-streams/general.any.js b/testing/web-platform/tests/streams/readable-streams/general.any.js
new file mode 100644
index 0000000000..2a32b27943
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/general.any.js
@@ -0,0 +1,840 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+test(() => {
+
+  new ReadableStream(); // ReadableStream constructed with no parameters
+  new ReadableStream({ }); // ReadableStream constructed with an empty object as parameter
+  new ReadableStream({ type: undefined }); // ReadableStream constructed with undefined type
+  new ReadableStream(undefined); // ReadableStream constructed with undefined as parameter
+
+  let x;
+  new ReadableStream(x); // ReadableStream constructed with an undefined variable as parameter
+
+}, 'ReadableStream can be constructed with no errors');
+
+test(() => {
+
+  assert_throws_js(TypeError, () => new ReadableStream(null), 'constructor should throw when the source is null');
+
+}, 'ReadableStream can\'t be constructed with garbage');
+
+test(() => {
+
+  assert_throws_js(TypeError, () => new ReadableStream({ type: null }),
+    'constructor should throw when the type is null');
+  assert_throws_js(TypeError, () => new ReadableStream({ type: '' }),
+    'constructor should throw when the type is empty string');
+  assert_throws_js(TypeError, () => new ReadableStream({ type: 'asdf' }),
+    'constructor should throw when the type is asdf');
+  assert_throws_exactly(
+    error1,
+    () => new ReadableStream({ type: { get toString() { throw error1; } } }),
+    'constructor should throw when ToString() throws'
+  );
+  assert_throws_exactly(
+    error1,
+    () => new ReadableStream({ type: { toString() { throw error1; } } }),
+    'constructor should throw when ToString() throws'
+  );
+
+}, 'ReadableStream can\'t be constructed with an invalid type');
+
+test(() => {
+
+  assert_throws_js(TypeError, () => {
+    new ReadableStream({ start: 'potato' });
+  }, 'constructor should throw when start is not a function');
+
+}, 'ReadableStream constructor should throw for non-function start arguments');
+
+test(() => {
+
+  assert_throws_js(TypeError, () => new ReadableStream({ cancel: '2' }), 'constructor should throw');
+
+}, 'ReadableStream constructor will not tolerate initial garbage as cancel argument');
+
+test(() => {
+
+  assert_throws_js(TypeError, () => new ReadableStream({ pull: { } }), 'constructor should throw');
+
+}, 'ReadableStream constructor will not tolerate initial garbage as pull argument');
+
+test(() => {
+
+  let startCalled = false;
+
+  const source = {
+    start() {
+      assert_equals(this, source, 'source is this during start');
+      startCalled = true;
+    }
+  };
+
+  new ReadableStream(source);
+  assert_true(startCalled);
+
+}, 'ReadableStream start should be called with the proper thisArg');
+
+test(() => {
+
+  let startCalled = false;
+  const source = {
+    start(controller) {
+      const properties = ['close', 'constructor', 'desiredSize', 'enqueue', 'error'];
+      assert_array_equals(Object.getOwnPropertyNames(Object.getPrototypeOf(controller)).sort(), properties,
+        'prototype should have the right properties');
+
+      controller.test = '';
+      assert_array_equals(Object.getOwnPropertyNames(Object.getPrototypeOf(controller)).sort(), properties,
+        'prototype should still have the right properties');
+      assert_not_equals(Object.getOwnPropertyNames(controller).indexOf('test'), -1,
+        '"test" should be a property of the controller');
+
+      startCalled = true;
+    }
+  };
+
+  new ReadableStream(source);
+  assert_true(startCalled);
+
+}, 'ReadableStream start controller parameter should be extensible');
+
+test(() => {
+  (new ReadableStream()).getReader(undefined);
+  (new ReadableStream()).getReader({});
+  (new ReadableStream()).getReader({ mode: undefined, notmode: 'ignored' });
+  assert_throws_js(TypeError, () => (new ReadableStream()).getReader({ mode: 'potato' }));
+}, 'default ReadableStream getReader() should only accept mode:undefined');
+
+promise_test(() => {
+
+  function SimpleStreamSource() {}
+  let resolve;
+  const promise = new Promise(r => resolve = r);
+  SimpleStreamSource.prototype = {
+    start: resolve
+  };
+
+  new ReadableStream(new SimpleStreamSource());
+  return promise;
+
+}, 'ReadableStream should be able to call start method within prototype chain of its source');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      return delay(5).then(() => {
+        c.enqueue('a');
+        c.close();
+      });
+    }
+  });
+
+  const reader = rs.getReader();
+  return reader.read().then(r => {
+    assert_object_equals(r, { value: 'a', done: false }, 'value read should be the one enqueued');
+    return reader.closed;
+  });
+
+}, 'ReadableStream start should be able to return a promise');
+
+promise_test(() => {
+
+  const theError = new Error('rejected!');
+  const rs = new ReadableStream({
+    start() {
+      return delay(1).then(() => {
+        throw theError;
+      });
+    }
+  });
+
+  return rs.getReader().closed.then(() => {
+    assert_unreached('closed promise should be rejected');
+  }, e => {
+    assert_equals(e, theError, 'promise should be rejected with the same error');
+  });
+
+}, 'ReadableStream start should be able to return a promise and reject it');
+
+promise_test(() => {
+
+  const objects = [
+    { potato: 'Give me more!' },
+    'test',
+    1
+  ];
+
+  const rs = new ReadableStream({
+    start(c) {
+      for (const o of objects) {
+        c.enqueue(o);
+      }
+      c.close();
+    }
+  });
+
+  const reader = rs.getReader();
+
+  return Promise.all([reader.read(), reader.read(), reader.read(), reader.closed]).then(r => {
+    assert_object_equals(r[0], { value: objects[0], done: false }, 'value read should be the one enqueued');
+    assert_object_equals(r[1], { value: objects[1], done: false }, 'value read should be the one enqueued');
+    assert_object_equals(r[2], { value: objects[2], done: false }, 'value read should be the one enqueued');
+  });
+
+}, 'ReadableStream should be able to enqueue different objects.');
+
+promise_test(() => {
+
+  const error = new Error('pull failure');
+  const rs = new ReadableStream({
+    pull() {
+      return Promise.reject(error);
+    }
+  });
+
+  const reader = rs.getReader();
+
+  let closed = false;
+  let read = false;
+
+  return Promise.all([
+    reader.closed.then(() => {
+      assert_unreached('closed should be rejected');
+    }, e => {
+      closed = true;
+      assert_false(read);
+      assert_equals(e, error, 'closed should be rejected with the thrown error');
+    }),
+    reader.read().then(() => {
+      assert_unreached('read() should be rejected');
+    }, e => {
+      read = true;
+      assert_true(closed);
+      assert_equals(e, error, 'read() should be rejected with the thrown error');
+    })
+  ]);
+
+}, 'ReadableStream: if pull rejects, it should error the stream');
+
+promise_test(() => {
+
+  let pullCount = 0;
+
+  new ReadableStream({
+    pull() {
+      pullCount++;
+    }
+  });
+
+  return flushAsyncEvents().then(() => {
+    assert_equals(pullCount, 1, 'pull should be called once start finishes');
+    return delay(10);
+  }).then(() => {
+    assert_equals(pullCount, 1, 'pull should be called exactly once');
+  });
+
+}, 'ReadableStream: should only call pull once upon starting the stream');
+
+promise_test(() => {
+
+  let pullCount = 0;
+
+  const rs = new ReadableStream({
+    pull(c) {
+      // Don't enqueue immediately after start. We want the stream to be empty when we call .read() on it.
+      if (pullCount > 0) {
+        c.enqueue(pullCount);
+      }
+      ++pullCount;
+    }
+  });
+
+  return flushAsyncEvents().then(() => {
+    assert_equals(pullCount, 1, 'pull should be called once start finishes');
+  }).then(() => {
+    const reader = rs.getReader();
+    const read = reader.read();
+    assert_equals(pullCount, 2, 'pull should be called when read is called');
+    return read;
+  }).then(result => {
+    assert_equals(pullCount, 3, 'pull should be called again in reaction to calling read');
+    assert_object_equals(result, { value: 1, done: false }, 'the result read should be the one enqueued');
+  });
+
+}, 'ReadableStream: should call pull when trying to read from a started, empty stream');
+
+promise_test(() => {
+
+  let pullCount = 0;
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+    },
+    pull() {
+      pullCount++;
+    }
+  });
+
+  const read = rs.getReader().read();
+  assert_equals(pullCount, 0, 'calling read() should not cause pull to be called yet');
+
+  return flushAsyncEvents().then(() => {
+    assert_equals(pullCount, 1, 'pull should be called once start finishes');
+    return read;
+  }).then(r => {
+    assert_object_equals(r, { value: 'a', done: false }, 'first read() should return first chunk');
+    assert_equals(pullCount, 1, 'pull should not have been called again');
+    return delay(10);
+  }).then(() => {
+    assert_equals(pullCount, 1, 'pull should be called exactly once');
+  });
+
+}, 'ReadableStream: should only call pull once on a non-empty stream read from before start fulfills');
+
+promise_test(() => {
+
+  let pullCount = 0;
+  const startPromise = Promise.resolve();
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+    },
+    pull() {
+      pullCount++;
+    }
+  });
+
+  return flushAsyncEvents().then(() => {
+    assert_equals(pullCount, 0, 'pull should not be called once start finishes, since the queue is full');
+
+    const read = rs.getReader().read();
+    assert_equals(pullCount, 1, 'calling read() should cause pull to be called immediately');
+    return read;
+  }).then(r => {
+    assert_object_equals(r, { value: 'a', done: false }, 'first read() should return first chunk');
+    return delay(10);
+  }).then(() => {
+    assert_equals(pullCount, 1, 'pull should be called exactly once');
+  });
+
+}, 'ReadableStream: should only call pull once on a non-empty stream read from after start fulfills');
+
+promise_test(() => {
+
+  let pullCount = 0;
+  let controller;
+
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      ++pullCount;
+    }
+  });
+
+  const reader = rs.getReader();
+  return flushAsyncEvents().then(() => {
+    assert_equals(pullCount, 1, 'pull should have been called once by the time the stream starts');
+
+    controller.enqueue('a');
+    assert_equals(pullCount, 1, 'pull should not have been called again after enqueue');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(pullCount, 2, 'pull should have been called again after read');
+
+    return delay(10);
+  }).then(() => {
+    assert_equals(pullCount, 2, 'pull should be called exactly twice');
+  });
+}, 'ReadableStream: should call pull in reaction to read()ing the last chunk, if not draining');
+
+promise_test(() => {
+
+  let pullCount = 0;
+  let controller;
+
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    pull() {
+      ++pullCount;
+    }
+  });
+
+  const reader = rs.getReader();
+
+  return flushAsyncEvents().then(() => {
+    assert_equals(pullCount, 1, 'pull should have been called once by the time the stream starts');
+
+    controller.enqueue('a');
+    assert_equals(pullCount, 1, 'pull should not have been called again after enqueue');
+
+    controller.close();
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(pullCount, 1, 'pull should not have been called a second time after read');
+
+    return delay(10);
+  }).then(() => {
+    assert_equals(pullCount, 1, 'pull should be called exactly once');
+  });
+
+}, 'ReadableStream: should not call pull() in reaction to read()ing the last chunk, if draining');
+
+promise_test(() => {
+
+  let resolve;
+  let returnedPromise;
+  let timesCalled = 0;
+
+  const rs = new ReadableStream({
+    pull(c) {
+      c.enqueue(++timesCalled);
+      returnedPromise = new Promise(r => resolve = r);
+      return returnedPromise;
+    }
+  });
+  const reader = rs.getReader();
+
+  return reader.read()
+  .then(result1 => {
+    assert_equals(timesCalled, 1,
+      'pull should have been called once after start, but not yet have been called a second time');
+    assert_object_equals(result1, { value: 1, done: false }, 'read() should fulfill with the enqueued value');
+
+    return delay(10);
+  }).then(() => {
+    assert_equals(timesCalled, 1, 'after 10 ms, pull should still only have been called once');
+
+    resolve();
+    return returnedPromise;
+  }).then(() => {
+    assert_equals(timesCalled, 2,
+      'after the promise returned by pull is fulfilled, pull should be called a second time');
+  });
+
+}, 'ReadableStream: should not call pull until the previous pull call\'s promise fulfills');
+
+promise_test(() => {
+
+  let timesCalled = 0;
+
+  const rs = new ReadableStream(
+    {
+      start(c) {
+        c.enqueue('a');
+        c.enqueue('b');
+        c.enqueue('c');
+      },
+      pull() {
+        ++timesCalled;
+      }
+    },
+    {
+      size() {
+        return 1;
+      },
+      highWaterMark: Infinity
+    }
+  );
+  const reader = rs.getReader();
+
+  return flushAsyncEvents().then(() => {
+    return reader.read();
+  }).then(result1 => {
+    assert_object_equals(result1, { value: 'a', done: false }, 'first chunk should be as expected');
+
+    return reader.read();
+  }).then(result2 => {
+    assert_object_equals(result2, { value: 'b', done: false }, 'second chunk should be as expected');
+
+    return reader.read();
+  }).then(result3 => {
+    assert_object_equals(result3, { value: 'c', done: false }, 'third chunk should be as expected');
+
+    return delay(10);
+  }).then(() => {
+    // Once for after start, and once for every read.
+    assert_equals(timesCalled, 4, 'pull() should be called exactly four times');
+  });
+
+}, 'ReadableStream: should pull after start, and after every read');
+
+promise_test(() => {
+
+  let timesCalled = 0;
+  const startPromise = Promise.resolve();
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.close();
+      return startPromise;
+    },
+    pull() {
+      ++timesCalled;
+    }
+  });
+
+  const reader = rs.getReader();
+  return startPromise.then(() => {
+    assert_equals(timesCalled, 0, 'after start finishes, pull should not have been called');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(timesCalled, 0, 'reading should not have triggered a pull call');
+
+    return reader.closed;
+  }).then(() => {
+    assert_equals(timesCalled, 0, 'stream should have closed with still no calls to pull');
+  });
+
+}, 'ReadableStream: should not call pull after start if the stream is now closed');
+
+promise_test(() => {
+
+  let timesCalled = 0;
+  let resolve;
+  const ready = new Promise(r => resolve = r);
+
+  new ReadableStream(
+    {
+      start() {},
+      pull(c) {
+        c.enqueue(++timesCalled);
+
+        if (timesCalled === 4) {
+          resolve();
+        }
+      }
+    },
+    {
+      size() {
+        return 1;
+      },
+      highWaterMark: 4
+    }
+  );
+
+  return ready.then(() => {
+    // after start: size = 0, pull()
+    // after enqueue(1): size = 1, pull()
+    // after enqueue(2): size = 2, pull()
+    // after enqueue(3): size = 3, pull()
+    // after enqueue(4): size = 4, do not pull
+    assert_equals(timesCalled, 4, 'pull() should have been called four times');
+  });
+
+}, 'ReadableStream: should call pull after enqueueing from inside pull (with no read requests), if strategy allows');
+
+promise_test(() => {
+
+  let pullCalled = false;
+
+  const rs = new ReadableStream({
+    pull(c) {
+      pullCalled = true;
+      c.close();
+    }
+  });
+
+  const reader = rs.getReader();
+  return reader.closed.then(() => {
+    assert_true(pullCalled);
+  });
+
+}, 'ReadableStream pull should be able to close a stream.');
+
+promise_test(t => {
+
+  const controllerError = { name: 'controller error' };
+
+  const rs = new ReadableStream({
+    pull(c) {
+      c.error(controllerError);
+    }
+  });
+
+  return promise_rejects_exactly(t, controllerError, rs.getReader().closed);
+
+}, 'ReadableStream pull should be able to error a stream.');
+
+promise_test(t => {
+
+  const controllerError = { name: 'controller error' };
+  const thrownError = { name: 'thrown error' };
+
+  const rs = new ReadableStream({
+    pull(c) {
+      c.error(controllerError);
+      throw thrownError;
+    }
+  });
+
+  return promise_rejects_exactly(t, controllerError, rs.getReader().closed);
+
+}, 'ReadableStream pull should be able to error a stream and throw.');
+
+test(() => {
+
+  let startCalled = false;
+
+  new ReadableStream({
+    start(c) {
+      assert_equals(c.enqueue('a'), undefined, 'the first enqueue should return undefined');
+      c.close();
+
+      assert_throws_js(TypeError, () => c.enqueue('b'), 'enqueue after close should throw a TypeError');
+      startCalled = true;
+    }
+  });
+
+  assert_true(startCalled);
+
+}, 'ReadableStream: enqueue should throw when the stream is readable but draining');
+
+test(() => {
+
+  let startCalled = false;
+
+  new ReadableStream({
+    start(c) {
+      c.close();
+
+      assert_throws_js(TypeError, () => c.enqueue('a'), 'enqueue after close should throw a TypeError');
+      startCalled = true;
+    }
+  });
+
+  assert_true(startCalled);
+
+}, 'ReadableStream: enqueue should throw when the stream is closed');
+
+promise_test(() => {
+
+  let startCalled = 0;
+  let pullCalled = 0;
+  let cancelCalled = 0;
+
+  /* eslint-disable no-use-before-define */
+  class Source {
+    start(c) {
+      startCalled++;
+      assert_equals(this, theSource, 'start() should be called with the correct this');
+      c.enqueue('a');
+    }
+
+    pull() {
+      pullCalled++;
+      assert_equals(this, theSource, 'pull() should be called with the correct this');
+    }
+
+    cancel() {
+      cancelCalled++;
+      assert_equals(this, theSource, 'cancel() should be called with the correct this');
+    }
+  }
+  /* eslint-enable no-use-before-define */
+
+  const theSource = new Source();
+  theSource.debugName = 'the source object passed to the constructor'; // makes test failures easier to diagnose
+
+  const rs = new ReadableStream(theSource);
+  const reader = rs.getReader();
+
+  return reader.read().then(() => {
+    reader.releaseLock();
+    rs.cancel();
+    assert_equals(startCalled, 1);
+    assert_equals(pullCalled, 1);
+    assert_equals(cancelCalled, 1);
+    return rs.getReader().closed;
+  });
+
+}, 'ReadableStream: should call underlying source methods as methods');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      assert_equals(c.desiredSize, 10, 'desiredSize must start at highWaterMark');
+      c.close();
+      assert_equals(c.desiredSize, 0, 'after closing, desiredSize must be 0');
+    }
+  }, {
+    highWaterMark: 10
+  });
+}, 'ReadableStream: desiredSize when closed');
+
+test(() => {
+  new ReadableStream({
+    start(c) {
+      assert_equals(c.desiredSize, 10, 'desiredSize must start at highWaterMark');
+      c.error();
+      assert_equals(c.desiredSize, null, 'after erroring, desiredSize must be null');
+    }
+  }, {
+    highWaterMark: 10
+  });
+}, 'ReadableStream: desiredSize when errored');
+
+test(() => {
+  class Subclass extends ReadableStream {
+    extraFunction() {
+      return true;
+    }
+  }
+  assert_equals(
+      Object.getPrototypeOf(Subclass.prototype), ReadableStream.prototype,
+      'Subclass.prototype\'s prototype should be ReadableStream.prototype');
+  assert_equals(Object.getPrototypeOf(Subclass), ReadableStream,
+                'Subclass\'s prototype should be ReadableStream');
+  const sub = new Subclass();
+  assert_true(sub instanceof ReadableStream,
+              'Subclass object should be an instance of ReadableStream');
+  assert_true(sub instanceof Subclass,
+              'Subclass object should be an instance of Subclass');
+  const lockedGetter = Object.getOwnPropertyDescriptor(
+      ReadableStream.prototype, 'locked').get;
+  assert_equals(lockedGetter.call(sub), sub.locked,
+                'Subclass object should pass brand check');
+  assert_true(sub.extraFunction(),
+              'extraFunction() should be present on Subclass object');
+}, 'Subclassing ReadableStream should work');
+
+test(() => {
+
+  let startCalled = false;
+  new ReadableStream({
+    start(c) {
+      assert_equals(c.desiredSize, 1);
+      c.enqueue('a');
+      assert_equals(c.desiredSize, 0);
+      c.enqueue('b');
+      assert_equals(c.desiredSize, -1);
+      c.enqueue('c');
+      assert_equals(c.desiredSize, -2);
+      c.enqueue('d');
+      assert_equals(c.desiredSize, -3);
+      c.enqueue('e');
+      startCalled = true;
+    }
+  });
+
+  assert_true(startCalled);
+
+}, 'ReadableStream strategies: the default strategy should give desiredSize of 1 to start, decreasing by 1 per enqueue');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const reader = rs.getReader();
+
+  assert_equals(controller.desiredSize, 1, 'desiredSize should start at 1');
+  controller.enqueue('a');
+  assert_equals(controller.desiredSize, 0, 'desiredSize should decrease to 0 after first enqueue');
+
+  return reader.read().then(result1 => {
+    assert_object_equals(result1, { value: 'a', done: false }, 'first chunk read should be correct');
+
+    assert_equals(controller.desiredSize, 1, 'desiredSize should go up to 1 after the first read');
+    controller.enqueue('b');
+    assert_equals(controller.desiredSize, 0, 'desiredSize should go down to 0 after the second enqueue');
+
+    return reader.read();
+  }).then(result2 => {
+    assert_object_equals(result2, { value: 'b', done: false }, 'second chunk read should be correct');
+
+    assert_equals(controller.desiredSize, 1, 'desiredSize should go up to 1 after the second read');
+    controller.enqueue('c');
+    assert_equals(controller.desiredSize, 0, 'desiredSize should go down to 0 after the third enqueue');
+
+    return reader.read();
+  }).then(result3 => {
+    assert_object_equals(result3, { value: 'c', done: false }, 'third chunk read should be correct');
+
+    assert_equals(controller.desiredSize, 1, 'desiredSize should go up to 1 after the third read');
+    controller.enqueue('d');
+    assert_equals(controller.desiredSize, 0, 'desiredSize should go down to 0 after the fourth enqueue');
+  });
+
+}, 'ReadableStream strategies: the default strategy should continue giving desiredSize of 1 if the chunks are read immediately');
+
+promise_test(t => {
+
+  const randomSource = new RandomPushSource(8);
+
+  const rs = new ReadableStream({
+    start(c) {
+      assert_equals(typeof c, 'object', 'c should be an object in start');
+      assert_equals(typeof c.enqueue, 'function', 'enqueue should be a function in start');
+      assert_equals(typeof c.close, 'function', 'close should be a function in start');
+      assert_equals(typeof c.error, 'function', 'error should be a function in start');
+
+      randomSource.ondata = t.step_func(chunk => {
+        if (!c.enqueue(chunk) <= 0) {
+          randomSource.readStop();
+        }
+      });
+
+      randomSource.onend = c.close.bind(c);
+      randomSource.onerror = c.error.bind(c);
+    },
+
+    pull(c) {
+      assert_equals(typeof c, 'object', 'c should be an object in pull');
+      assert_equals(typeof c.enqueue, 'function', 'enqueue should be a function in pull');
+      assert_equals(typeof c.close, 'function', 'close should be a function in pull');
+
+      randomSource.readStart();
+    }
+  });
+
+  return readableStreamToArray(rs).then(chunks => {
+    assert_equals(chunks.length, 8, '8 chunks should be read');
+    for (const chunk of chunks) {
+      assert_equals(chunk.length, 128, 'chunk should have 128 bytes');
+    }
+  });
+
+}, 'ReadableStream integration test: adapting a random push source');
+
+promise_test(() => {
+
+  const rs = sequentialReadableStream(10);
+
+  return readableStreamToArray(rs).then(chunks => {
+    assert_true(rs.source.closed, 'source should be closed after all chunks are read');
+    assert_array_equals(chunks, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 'the expected 10 chunks should be read');
+  });
+
+}, 'ReadableStream integration test: adapting a sync pull source');
+
+promise_test(() => {
+
+  const rs = sequentialReadableStream(10, { async: true });
+
+  return readableStreamToArray(rs).then(chunks => {
+    assert_true(rs.source.closed, 'source should be closed after all chunks are read');
+    assert_array_equals(chunks, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 'the expected 10 chunks should be read');
+  });
+
+}, 'ReadableStream integration test: adapting an async pull source');
diff --git a/testing/web-platform/tests/streams/readable-streams/global.html b/testing/web-platform/tests/streams/readable-streams/global.html
new file mode 100644
index 0000000000..08665d318e
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/global.html
@@ -0,0 +1,162 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Ensure Stream objects are created in expected globals. </title>
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body></body>
+<script>
+// These tests are loosely derived from Gecko's readable-stream-globals.js,
+// which is a test case designed around the JS Streams implementation.
+//
+// Unlike in JS Streams, where function calls switch realms and change
+// the resulting global of the resulting objects, in WebIDL streams,
+// the global of an object is (currently underspecified, but) intended
+// to be the "Relevant Global" of the 'this' object.
+//
+// See:
+// https://html.spec.whatwg.org/multipage/webappapis.html#relevant
+// https://github.com/whatwg/streams/issues/1213
+"use strict"
+
+const iframe = document.createElement("iframe")
+document.body.append(iframe)
+
+const otherGlobal = iframe.contentWindow;
+const OtherReadableStream = otherGlobal.ReadableStream
+const OtherReadableStreamDefaultReader = otherGlobal.ReadableStreamDefaultReader;
+const OtherReadableStreamDefaultController = otherGlobal.ReadableStreamDefaultController;
+
+promise_test(async () => {
+
+    // Controllers
+    let controller;
+    let otherController;
+
+    // Get Stream Prototypes and controllers.
+    let streamController;
+    let stream = new ReadableStream({start(c) { streamController = c; }});
+
+    const callReaderThisGlobal = OtherReadableStream.prototype.getReader.call(stream);
+    const newReaderOtherGlobal = new OtherReadableStreamDefaultReader(new ReadableStream());
+
+    // Relevant Global Checking.
+    assert_equals(callReaderThisGlobal instanceof ReadableStreamDefaultReader, true, "reader was created in this global (.call)");
+    assert_equals(newReaderOtherGlobal instanceof ReadableStreamDefaultReader, false, "reader was created in other global (new)");
+
+    assert_equals(callReaderThisGlobal instanceof OtherReadableStreamDefaultReader, false, "reader isn't coming from other global (.call)" );
+    assert_equals(newReaderOtherGlobal instanceof OtherReadableStreamDefaultReader, true, "reader isn't coming from other global (new)");
+
+    assert_equals(otherController instanceof ReadableStreamDefaultController, false, "otherController should come from other gloal")
+
+
+    const request = callReaderThisGlobal.read();
+    assert_equals(request instanceof Promise, true, "Promise comes from this global");
+
+    streamController.close();
+    const requestResult = await request;
+    assert_equals(requestResult instanceof Object, true, "returned object comes from this global");
+}, "Stream objects created in expected globals")
+
+promise_test(async () => {
+    const stream = new ReadableStream();
+    const otherReader = new OtherReadableStreamDefaultReader(stream);
+    const cancelPromise = ReadableStreamDefaultReader.prototype.cancel.call(otherReader);
+    assert_equals(cancelPromise instanceof Promise, true, "Cancel promise comes from the same global as the stream");
+    assert_equals(await cancelPromise, undefined, "Cancel promise resolves to undefined");
+}, "Cancel promise is created in same global as stream")
+
+// Refresh the streams and controllers.
+function getFreshInstances() {
+    let controller;
+    let otherController;
+    let stream = new ReadableStream({
+        start(c) {
+            controller = c;
+        }
+    });
+
+    new OtherReadableStream({
+        start(c) {
+            otherController = c;
+        }
+    });
+
+    return {stream, controller, otherController}
+}
+
+
+promise_test(async () => {
+    // Test closed promise on reader from another global (connected to a this-global stream)
+    const {stream, controller, otherController} = getFreshInstances();
+
+    const otherReader = new OtherReadableStreamDefaultReader(stream);
+    const closedPromise = otherReader.closed;
+    assert_equals(closedPromise instanceof otherGlobal.Promise, true, "Closed promise in other global.");
+}, "Closed Promise in correct global");
+
+promise_test(async () => {
+    const {stream, controller, otherController} = getFreshInstances();
+
+    const otherReader = OtherReadableStream.prototype.getReader.call(stream);
+    assert_equals(otherReader instanceof ReadableStreamDefaultReader, true, "Reader comes from this global")
+    const request = otherReader.read();
+    assert_equals(request instanceof Promise, true, "Promise still comes from stream's realm (this realm)");
+    otherController.close.call(controller);
+    assert_equals((await request) instanceof otherGlobal.Object, true, "Object comes from other realm");
+}, "Reader objects in correct global");
+
+
+promise_test(async () => {
+    const {stream, controller, otherController} = getFreshInstances();
+    assert_equals(controller.desiredSize, 1, "Desired size is expected");
+    Object.defineProperty(controller, "desiredSize",
+        Object.getOwnPropertyDescriptor(OtherReadableStreamDefaultController.prototype, "desiredSize"));
+    assert_equals(controller.desiredSize, 1, "Grafting getter from other prototype still returns desired size");
+}, "Desired size can be grafted from one prototype to another");
+
+promise_test(async () => {
+    const {stream, controller, otherController} = getFreshInstances();
+
+    // Make sure the controller close method returns the correct TypeError
+    const enqueuedError = { name: "enqueuedError" };
+    controller.error(enqueuedError);
+
+    assert_throws_js(TypeError, () => controller.close(),  "Current Global controller");
+    assert_throws_js(otherGlobal.TypeError, () => otherController.close.call(controller),  "Other global controller");
+}, "Closing errored stream throws object in appropriate global")
+
+promise_test(async () => {
+    const {otherController} = getFreshInstances();
+    // We can enqueue chunks from multiple globals
+    const chunk = { name: "chunk" };
+
+    let controller;
+    const stream = new ReadableStream({ start(c) { controller = c; } }, { size() {return 1} });
+    otherController.enqueue.call(controller, chunk);
+    otherController.enqueue.call(controller, new otherGlobal.Uint8Array(10));
+    controller.enqueue(new otherGlobal.Uint8Array(10));
+}, "Can enqueue chunks from multiple globals")
+
+promise_test(async () => {
+    const {stream, controller, otherController} = getFreshInstances();
+    const chunk = { name: "chunk" };
+
+    // We get the correct type errors out of a closed stream.
+    controller.close();
+    assert_throws_js(TypeError, () => controller.enqueue(new otherGlobal.Uint8Array(10)));
+    assert_throws_js(otherGlobal.TypeError, () => otherController.enqueue.call(controller, chunk));
+    assert_throws_js(otherGlobal.TypeError, () => otherController.enqueue.call(controller, new otherGlobal.Uint8Array(10)));
+}, "Correct errors and globals for closed streams");
+
+
+promise_test(async () => {
+    const {stream, controller, otherController} = getFreshInstances();
+    // Branches out of tee are in the correct global
+
+    const [branch1, branch2] = otherGlobal.ReadableStream.prototype.tee.call(stream);
+    assert_equals(branch1 instanceof ReadableStream, true, "Branch created in this global (as stream is in this global)");
+    assert_equals(branch2 instanceof ReadableStream, true, "Branch created in this global (as stream is in this global)");
+}, "Tee Branches in correct global");
+</script>
diff --git a/testing/web-platform/tests/streams/readable-streams/owning-type-message-port.any.js b/testing/web-platform/tests/streams/readable-streams/owning-type-message-port.any.js
new file mode 100644
index 0000000000..e9961ce042
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/owning-type-message-port.any.js
@@ -0,0 +1,49 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+'use strict';
+
+promise_test(async () => {
+  const channel = new MessageChannel;
+  const port1 = channel.port1;
+  const port2 = channel.port2;
+
+  const source = {
+    start(controller) {
+      controller.enqueue(port1, { transfer : [ port1 ] });
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+
+  const chunk = await stream.getReader().read();
+
+  assert_not_equals(chunk.value, port1);
+
+  let promise = new Promise(resolve => port2.onmessage = e => resolve(e.data));
+  chunk.value.postMessage("toPort2");
+  assert_equals(await promise, "toPort2");
+
+  promise = new Promise(resolve => chunk.value.onmessage = e => resolve(e.data));
+  port2.postMessage("toPort1");
+  assert_equals(await promise, "toPort1");
+}, 'Transferred MessageChannel works as expected');
+
+promise_test(async t => {
+  const channel = new MessageChannel;
+  const port1 = channel.port1;
+  const port2 = channel.port2;
+
+  const source = {
+    start(controller) {
+      controller.enqueue({ port1 }, { transfer : [ port1 ] });
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  const [clone1, clone2] = stream.tee();
+
+  await promise_rejects_dom(t, "DataCloneError", clone2.getReader().read());
+}, 'Second branch of owning ReadableStream tee should end up into errors with transfer only values');
diff --git a/testing/web-platform/tests/streams/readable-streams/owning-type-video-frame.any.js b/testing/web-platform/tests/streams/readable-streams/owning-type-video-frame.any.js
new file mode 100644
index 0000000000..ec01fda0b3
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/owning-type-video-frame.any.js
@@ -0,0 +1,128 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+'use strict';
+
+function createVideoFrame()
+{
+  let init = {
+    format: 'I420',
+    timestamp: 1234,
+    codedWidth: 4,
+    codedHeight: 2
+  };
+  let data = new Uint8Array([
+    1, 2, 3, 4, 5, 6, 7, 8,  // y
+    1, 2,                    // u
+    1, 2,                    // v
+  ]);
+
+  return new VideoFrame(data, init);
+}
+
+promise_test(async () => {
+  const videoFrame = createVideoFrame();
+  videoFrame.test = 1;
+  const source = {
+    start(controller) {
+      assert_equals(videoFrame.format, 'I420');
+      controller.enqueue(videoFrame, { transfer : [ videoFrame ] });
+      assert_equals(videoFrame.format, null);
+      assert_equals(videoFrame.test, 1);
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  // Cancelling the stream should close all video frames, thus no console messages of GCing VideoFrames should happen.
+  stream.cancel();
+}, 'ReadableStream of type owning should close serialized chunks');
+
+promise_test(async () => {
+  const videoFrame = createVideoFrame();
+  videoFrame.test = 1;
+  const source = {
+    start(controller) {
+      assert_equals(videoFrame.format, 'I420');
+      controller.enqueue({ videoFrame }, { transfer : [ videoFrame ] });
+      assert_equals(videoFrame.format, null);
+      assert_equals(videoFrame.test, 1);
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  const reader = stream.getReader();
+
+  const chunk = await reader.read();
+  assert_equals(chunk.value.videoFrame.format, 'I420');
+  assert_equals(chunk.value.videoFrame.test, undefined);
+
+  chunk.value.videoFrame.close();
+}, 'ReadableStream of type owning should transfer JS chunks with transferred values');
+
+promise_test(async t => {
+  const videoFrame = createVideoFrame();
+  videoFrame.close();
+  const source = {
+    start(controller) {
+      assert_throws_dom("DataCloneError", () => controller.enqueue(videoFrame, { transfer : [ videoFrame ] }));
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  const reader = stream.getReader();
+
+  await promise_rejects_dom(t, "DataCloneError", reader.read());
+}, 'ReadableStream of type owning should error when trying to enqueue not serializable values');
+
+promise_test(async () => {
+  const videoFrame = createVideoFrame();
+  const source = {
+    start(controller) {
+      controller.enqueue(videoFrame, { transfer : [ videoFrame ] });
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  const [clone1, clone2] = stream.tee();
+
+  const chunk1 = await clone1.getReader().read();
+  const chunk2 = await clone2.getReader().read();
+
+  assert_equals(videoFrame.format, null);
+  assert_equals(chunk1.value.format, 'I420');
+  assert_equals(chunk2.value.format, 'I420');
+
+  chunk1.value.close();
+  chunk2.value.close();
+}, 'ReadableStream of type owning should clone serializable objects when teeing');
+
+promise_test(async () => {
+  const videoFrame = createVideoFrame();
+  videoFrame.test = 1;
+  const source = {
+    start(controller) {
+      assert_equals(videoFrame.format, 'I420');
+      controller.enqueue({ videoFrame }, { transfer : [ videoFrame ] });
+      assert_equals(videoFrame.format, null);
+      assert_equals(videoFrame.test, 1);
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  const [clone1, clone2] = stream.tee();
+
+  const chunk1 = await clone1.getReader().read();
+  const chunk2 = await clone2.getReader().read();
+
+  assert_equals(videoFrame.format, null);
+  assert_equals(chunk1.value.videoFrame.format, 'I420');
+  assert_equals(chunk2.value.videoFrame.format, 'I420');
+
+  chunk1.value.videoFrame.close();
+  chunk2.value.videoFrame.close();
+}, 'ReadableStream of type owning should clone JS Objects with serializables when teeing');
diff --git a/testing/web-platform/tests/streams/readable-streams/owning-type.any.js b/testing/web-platform/tests/streams/readable-streams/owning-type.any.js
new file mode 100644
index 0000000000..27a3dda894
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/owning-type.any.js
@@ -0,0 +1,91 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+'use strict';
+
+test(() => {
+  new ReadableStream({ type: 'owning' }); // ReadableStream constructed with 'owning' type
+}, 'ReadableStream can be constructed with owning type');
+
+test(() => {
+  let startCalled = false;
+
+  const source = {
+    start(controller) {
+      assert_equals(this, source, 'source is this during start');
+      assert_true(controller instanceof ReadableStreamDefaultController, 'default controller');
+      startCalled = true;
+    },
+    type: 'owning'
+  };
+
+  new ReadableStream(source);
+  assert_true(startCalled);
+}, 'ReadableStream of type owning should call start with a ReadableStreamDefaultController');
+
+test(() => {
+  let startCalled = false;
+
+  const source = {
+    start(controller) {
+      controller.enqueue("a", { transfer: [] });
+      controller.enqueue("a", { transfer: undefined });
+      startCalled = true;
+    },
+    type: 'owning'
+  };
+
+  new ReadableStream(source);
+  assert_true(startCalled);
+}, 'ReadableStream should be able to call enqueue with an empty transfer list');
+
+test(() => {
+  let startCalled = false;
+
+  const uint8Array = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8]);
+  const buffer = uint8Array.buffer;
+  let source = {
+    start(controller) {
+      startCalled = true;
+      assert_throws_js(TypeError, () => { controller.enqueue(buffer, { transfer : [ buffer ] }); }, "transfer list is not empty");
+    }
+  };
+
+  new ReadableStream(source);
+  assert_true(startCalled);
+
+  startCalled = false;
+  source = {
+    start(controller) {
+      startCalled = true;
+      assert_throws_js(TypeError, () => { controller.enqueue(buffer, { get transfer() { throw new TypeError(); } }) }, "getter throws");
+    }
+  };
+
+  new ReadableStream(source);
+  assert_true(startCalled);
+}, 'ReadableStream should check transfer parameter');
+
+promise_test(async () => {
+  const uint8Array = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8]);
+  const buffer = uint8Array.buffer;
+  buffer.test = 1;
+  const source = {
+    start(controller) {
+      assert_equals(buffer.byteLength, 8);
+      controller.enqueue(buffer, { transfer : [ buffer ] });
+      assert_equals(buffer.byteLength, 0);
+      assert_equals(buffer.test, 1);
+    },
+    type: 'owning'
+  };
+
+  const stream = new ReadableStream(source);
+  const reader = stream.getReader();
+
+  const chunk = await reader.read();
+
+  assert_not_equals(chunk.value, buffer);
+  assert_equals(chunk.value.byteLength, 8);
+  assert_equals(chunk.value.test, undefined);
+}, 'ReadableStream of type owning should transfer enqueued chunks');
diff --git a/testing/web-platform/tests/streams/readable-streams/patched-global.any.js b/testing/web-platform/tests/streams/readable-streams/patched-global.any.js
new file mode 100644
index 0000000000..a64a054a97
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/patched-global.any.js
@@ -0,0 +1,142 @@
+// META: global=window,worker
+'use strict';
+
+// Tests which patch the global environment are kept separate to avoid
+// interfering with other tests.
+
+const ReadableStream_prototype_locked_get =
+      Object.getOwnPropertyDescriptor(ReadableStream.prototype, 'locked').get;
+
+// Verify that |rs| passes the brand check as a readable stream.
+function isReadableStream(rs) {
+  try {
+    ReadableStream_prototype_locked_get.call(rs);
+    return true;
+  } catch (e) {
+    return false;
+  }
+}
+
+test(t => {
+  const rs = new ReadableStream();
+
+  const trappedProperties = ['highWaterMark', 'size', 'start', 'type', 'mode'];
+  for (const property of trappedProperties) {
+    // eslint-disable-next-line no-extend-native, accessor-pairs
+    Object.defineProperty(Object.prototype, property, {
+      get() { throw new Error(`${property} getter called`); },
+      configurable: true
+    });
+  }
+  t.add_cleanup(() => {
+    for (const property of trappedProperties) {
+      delete Object.prototype[property];
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  assert_true(isReadableStream(branch1), 'branch1 should be a ReadableStream');
+  assert_true(isReadableStream(branch2), 'branch2 should be a ReadableStream');
+}, 'ReadableStream tee() should not touch Object.prototype properties');
+
+test(t => {
+  const rs = new ReadableStream();
+
+  const oldReadableStream = self.ReadableStream;
+
+  self.ReadableStream = function() {
+    throw new Error('ReadableStream called on global object');
+  };
+
+  t.add_cleanup(() => {
+    self.ReadableStream = oldReadableStream;
+  });
+
+  const [branch1, branch2] = rs.tee();
+
+  assert_true(isReadableStream(branch1), 'branch1 should be a ReadableStream');
+  assert_true(isReadableStream(branch2), 'branch2 should be a ReadableStream');
+}, 'ReadableStream tee() should not call the global ReadableStream');
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue(1);
+      c.enqueue(2);
+      c.enqueue(3);
+      c.close();
+    }
+  });
+
+  const oldReadableStreamGetReader = ReadableStream.prototype.getReader;
+
+  const ReadableStreamDefaultReader = (new ReadableStream()).getReader().constructor;
+  const oldDefaultReaderRead = ReadableStreamDefaultReader.prototype.read;
+  const oldDefaultReaderCancel = ReadableStreamDefaultReader.prototype.cancel;
+  const oldDefaultReaderReleaseLock = ReadableStreamDefaultReader.prototype.releaseLock;
+
+  self.ReadableStream.prototype.getReader = function() {
+    throw new Error('patched getReader() called');
+  };
+
+  ReadableStreamDefaultReader.prototype.read = function() {
+    throw new Error('patched read() called');
+  };
+  ReadableStreamDefaultReader.prototype.cancel = function() {
+    throw new Error('patched cancel() called');
+  };
+  ReadableStreamDefaultReader.prototype.releaseLock = function() {
+    throw new Error('patched releaseLock() called');
+  };
+
+  t.add_cleanup(() => {
+    self.ReadableStream.prototype.getReader = oldReadableStreamGetReader;
+
+    ReadableStreamDefaultReader.prototype.read = oldDefaultReaderRead;
+    ReadableStreamDefaultReader.prototype.cancel = oldDefaultReaderCancel;
+    ReadableStreamDefaultReader.prototype.releaseLock = oldDefaultReaderReleaseLock;
+  });
+
+  // read the first chunk, then cancel
+  for await (const chunk of rs) {
+    break;
+  }
+
+  // should be able to acquire a new reader
+  const reader = oldReadableStreamGetReader.call(rs);
+  // stream should be cancelled
+  await reader.closed;
+}, 'ReadableStream async iterator should use the original values of getReader() and ReadableStreamDefaultReader ' +
+   'methods');
+
+test(t => {
+  const oldPromiseThen = Promise.prototype.then;
+  Promise.prototype.then = () => {
+    throw new Error('patched then() called');
+  };
+  t.add_cleanup(() => {
+    Promise.prototype.then = oldPromiseThen;
+  });
+  const [branch1, branch2] = new ReadableStream().tee();
+  assert_true(isReadableStream(branch1), 'branch1 should be a ReadableStream');
+  assert_true(isReadableStream(branch2), 'branch2 should be a ReadableStream');
+}, 'tee() should not call Promise.prototype.then()');
+
+test(t => {
+  const oldPromiseThen = Promise.prototype.then;
+  Promise.prototype.then = () => {
+    throw new Error('patched then() called');
+  };
+  t.add_cleanup(() => {
+    Promise.prototype.then = oldPromiseThen;
+  });
+  let readableController;
+  const rs = new ReadableStream({
+    start(c) {
+      readableController = c;
+    }
+  });
+  const ws = new WritableStream();
+  rs.pipeTo(ws);
+  readableController.close();
+}, 'pipeTo() should not call Promise.prototype.then()');
diff --git a/testing/web-platform/tests/streams/readable-streams/read-task-handling.window.js b/testing/web-platform/tests/streams/readable-streams/read-task-handling.window.js
new file mode 100644
index 0000000000..2edc0ddddf
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/read-task-handling.window.js
@@ -0,0 +1,46 @@
+// META: global=window,worker
+'use strict';
+
+function performMicrotaskCheckpoint() {
+    document.createNodeIterator(document, -1, {
+        acceptNode() {
+            return NodeFilter.FILTER_ACCEPT;
+        }
+    }).nextNode();
+}
+
+test(() => {
+    // Add a getter for "then" that will incidentally be invoked
+    // during promise resolution.
+    Object.prototype.__defineGetter__('then', () => {
+        // Clean up behind ourselves.
+        delete Object.prototype.then;
+
+        // This promise should (like all promises) be resolved
+        // asynchronously.
+        var executed = false;
+        Promise.resolve().then(_ => { executed = true; });
+
+        // This shouldn't run microtasks!  They should only run
+        // after the fetch is resolved.
+        performMicrotaskCheckpoint();
+
+        // The fulfill handler above shouldn't have run yet.  If it has run,
+        // throw to reject this promise and fail the test.
+        assert_false(executed, "shouldn't have run microtasks yet");
+
+        // Otherwise act as if there's no "then" property so the promise
+        // fulfills and the test passes.
+        return undefined;
+    });
+
+    const readable = new ReadableStream({
+        pull(c) {
+            c.enqueue({});
+        }
+    }, { highWaterMark: 0 });
+
+    // Create a read request, incidentally resolving a promise with an
+    // object value, thereby invoking the getter installed above.
+    readable.getReader().read();
+}, "reading from a stream should occur in a microtask scope");
diff --git a/testing/web-platform/tests/streams/readable-streams/reentrant-strategies.any.js b/testing/web-platform/tests/streams/readable-streams/reentrant-strategies.any.js
new file mode 100644
index 0000000000..b4988bc243
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/reentrant-strategies.any.js
@@ -0,0 +1,264 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+// The size() function of the readable strategy can re-entrantly call back into the ReadableStream implementation. This
+// makes it risky to cache state across the call to ReadableStreamDefaultControllerEnqueue. These tests attempt to catch
+// such errors. They are separated from the other strategy tests because no real user code should ever do anything like
+// this.
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+promise_test(() => {
+  let controller;
+  let calls = 0;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      ++calls;
+      if (calls < 2) {
+        controller.enqueue('b');
+      }
+      return 1;
+    }
+  });
+  controller.enqueue('a');
+  controller.close();
+  return readableStreamToArray(rs)
+      .then(array => assert_array_equals(array, ['b', 'a'], 'array should contain two chunks'));
+}, 'enqueue() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      // The queue is empty.
+      controller.close();
+      // The state has gone from "readable" to "closed".
+      return 1;
+      // This chunk will be enqueued, but will be impossible to read because the state is already "closed".
+    }
+  });
+  controller.enqueue('a');
+  return readableStreamToArray(rs)
+      .then(array => assert_array_equals(array, [], 'array should contain no chunks'));
+  // The chunk 'a' is still in rs's queue. It is closed so 'a' cannot be read.
+}, 'close() inside size() should not crash');
+
+promise_test(() => {
+  let controller;
+  let calls = 0;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      ++calls;
+      if (calls === 2) {
+        // The queue contains one chunk.
+        controller.close();
+        // The state is still "readable", but closeRequest is now true.
+      }
+      return 1;
+    }
+  });
+  controller.enqueue('a');
+  controller.enqueue('b');
+  return readableStreamToArray(rs)
+      .then(array => assert_array_equals(array, ['a', 'b'], 'array should contain two chunks'));
+}, 'close request inside size() should work');
+
+promise_test(t => {
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      controller.error(error1);
+      return 1;
+    }
+  });
+  controller.enqueue('a');
+  return promise_rejects_exactly(t, error1, rs.getReader().read(), 'read() should reject');
+}, 'error() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      assert_equals(controller.desiredSize, 1, 'desiredSize should be 1');
+      return 1;
+    },
+    highWaterMark: 1
+  });
+  controller.enqueue('a');
+  controller.close();
+  return readableStreamToArray(rs)
+      .then(array => assert_array_equals(array, ['a'], 'array should contain one chunk'));
+}, 'desiredSize inside size() should work');
+
+promise_test(t => {
+  let cancelPromise;
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    },
+    cancel: t.step_func(reason => {
+      assert_equals(reason, error1, 'reason should be error1');
+      assert_throws_js(TypeError, () => controller.enqueue(), 'enqueue() should throw');
+    })
+  }, {
+    size() {
+      cancelPromise = rs.cancel(error1);
+      return 1;
+    },
+    highWaterMark: Infinity
+  });
+  controller.enqueue('a');
+  const reader = rs.getReader();
+  return Promise.all([
+    reader.closed,
+    cancelPromise
+  ]);
+}, 'cancel() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  let pipeToPromise;
+  const ws = recordingWritableStream();
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      if (!pipeToPromise) {
+        pipeToPromise = rs.pipeTo(ws);
+      }
+      return 1;
+    },
+    highWaterMark: 1
+  });
+  controller.enqueue('a');
+  assert_not_equals(pipeToPromise, undefined);
+
+  // Some pipeTo() implementations need an additional chunk enqueued in order for the first one to be processed. See
+  // https://github.com/whatwg/streams/issues/794 for background.
+  controller.enqueue('a');
+
+  // Give pipeTo() a chance to process the queued chunks.
+  return delay(0).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'a'], 'ws should contain two chunks');
+    controller.close();
+    return pipeToPromise;
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'a', 'close'], 'target should have been closed');
+  });
+}, 'pipeTo() inside size() should behave as expected');
+
+promise_test(() => {
+  let controller;
+  let readPromise;
+  let calls = 0;
+  let readResolved = false;
+  let reader;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      // This is triggered by controller.enqueue(). The queue is empty and there are no pending reads. This read is
+      // added to the list of pending reads.
+      readPromise = reader.read();
+      ++calls;
+      return 1;
+    },
+    highWaterMark: 0
+  });
+  reader = rs.getReader();
+  controller.enqueue('a');
+  readPromise.then(() => {
+    readResolved = true;
+  });
+  return flushAsyncEvents().then(() => {
+    assert_false(readResolved);
+    controller.enqueue('b');
+    assert_equals(calls, 1, 'size() should have been called once');
+    return delay(0);
+  }).then(() => {
+    assert_true(readResolved);
+    assert_equals(calls, 1, 'size() should only be called once');
+    return readPromise;
+  }).then(({ value, done }) => {
+    assert_false(done, 'done should be false');
+    // See https://github.com/whatwg/streams/issues/794 for why this chunk is not 'a'.
+    assert_equals(value, 'b', 'chunk should have been read');
+    assert_equals(calls, 1, 'calls should still be 1');
+    return reader.read();
+  }).then(({ value, done }) => {
+    assert_false(done, 'done should be false again');
+    assert_equals(value, 'a', 'chunk a should come after b');
+  });
+}, 'read() inside of size() should behave as expected');
+
+promise_test(() => {
+  let controller;
+  let reader;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      reader = rs.getReader();
+      return 1;
+    }
+  });
+  controller.enqueue('a');
+  return reader.read().then(({ value, done }) => {
+    assert_false(done, 'done should be false');
+    assert_equals(value, 'a', 'value should be a');
+  });
+}, 'getReader() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  let branch1;
+  let branch2;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, {
+    size() {
+      [branch1, branch2] = rs.tee();
+      return 1;
+    }
+  });
+  controller.enqueue('a');
+  assert_true(rs.locked, 'rs should be locked');
+  controller.close();
+  return Promise.all([
+    readableStreamToArray(branch1).then(array => assert_array_equals(array, ['a'], 'branch1 should have one chunk')),
+    readableStreamToArray(branch2).then(array => assert_array_equals(array, ['a'], 'branch2 should have one chunk'))
+  ]);
+}, 'tee() inside size() should work');
diff --git a/testing/web-platform/tests/streams/readable-streams/tee.any.js b/testing/web-platform/tests/streams/readable-streams/tee.any.js
new file mode 100644
index 0000000000..00397932f4
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/tee.any.js
@@ -0,0 +1,479 @@
+// META: global=window,worker
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+// META: script=../resources/rs-test-templates.js
+'use strict';
+
+test(() => {
+
+  const rs = new ReadableStream();
+  const result = rs.tee();
+
+  assert_true(Array.isArray(result), 'return value should be an array');
+  assert_equals(result.length, 2, 'array should have length 2');
+  assert_equals(result[0].constructor, ReadableStream, '0th element should be a ReadableStream');
+  assert_equals(result[1].constructor, ReadableStream, '1st element should be a ReadableStream');
+
+}, 'ReadableStream teeing: rs.tee() returns an array of two ReadableStreams');
+
+promise_test(t => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.close();
+    }
+  });
+
+  const branch = rs.tee();
+  const branch1 = branch[0];
+  const branch2 = branch[1];
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  reader2.closed.then(t.unreached_func('branch2 should not be closed'));
+
+  return Promise.all([
+    reader1.closed,
+    reader1.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'first chunk from branch1 should be correct');
+    }),
+    reader1.read().then(r => {
+      assert_object_equals(r, { value: 'b', done: false }, 'second chunk from branch1 should be correct');
+    }),
+    reader1.read().then(r => {
+      assert_object_equals(r, { value: undefined, done: true }, 'third read() from branch1 should be done');
+    }),
+    reader2.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'first chunk from branch2 should be correct');
+    })
+  ]);
+
+}, 'ReadableStream teeing: should be able to read one branch to the end without affecting the other');
+
+promise_test(() => {
+
+  const theObject = { the: 'test object' };
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue(theObject);
+    }
+  });
+
+  const branch = rs.tee();
+  const branch1 = branch[0];
+  const branch2 = branch[1];
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  return Promise.all([reader1.read(), reader2.read()]).then(values => {
+    assert_object_equals(values[0], values[1], 'the values should be equal');
+  });
+
+}, 'ReadableStream teeing: values should be equal across each branch');
+
+promise_test(t => {
+
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+    },
+    pull() {
+      throw theError;
+    }
+  });
+
+  const branches = rs.tee();
+  const reader1 = branches[0].getReader();
+  const reader2 = branches[1].getReader();
+
+  reader1.label = 'reader1';
+  reader2.label = 'reader2';
+
+  return Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed),
+    reader1.read().then(r => {
+      assert_object_equals(r, { value: 'a', done: false }, 'should be able to read the first chunk in branch1');
+    }),
+    reader1.read().then(r => {
+      assert_object_equals(r, { value: 'b', done: false }, 'should be able to read the second chunk in branch1');
+
+      return promise_rejects_exactly(t, theError, reader2.read());
+    })
+    .then(() => promise_rejects_exactly(t, theError, reader1.read()))
+  ]);
+
+}, 'ReadableStream teeing: errors in the source should propagate to both branches');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.close();
+    }
+  });
+
+  const branches = rs.tee();
+  const branch1 = branches[0];
+  const branch2 = branches[1];
+  branch1.cancel();
+
+  return Promise.all([
+    readableStreamToArray(branch1).then(chunks => {
+      assert_array_equals(chunks, [], 'branch1 should have no chunks');
+    }),
+    readableStreamToArray(branch2).then(chunks => {
+      assert_array_equals(chunks, ['a', 'b'], 'branch2 should have two chunks');
+    })
+  ]);
+
+}, 'ReadableStream teeing: canceling branch1 should not impact branch2');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.close();
+    }
+  });
+
+  const branches = rs.tee();
+  const branch1 = branches[0];
+  const branch2 = branches[1];
+  branch2.cancel();
+
+  return Promise.all([
+    readableStreamToArray(branch1).then(chunks => {
+      assert_array_equals(chunks, ['a', 'b'], 'branch1 should have two chunks');
+    }),
+    readableStreamToArray(branch2).then(chunks => {
+      assert_array_equals(chunks, [], 'branch2 should have no chunks');
+    })
+  ]);
+
+}, 'ReadableStream teeing: canceling branch2 should not impact branch1');
+
+templatedRSTeeCancel('ReadableStream teeing', (extras) => {
+  return new ReadableStream({ ...extras });
+});
+
+promise_test(t => {
+
+  let controller;
+  const stream = new ReadableStream({ start(c) { controller = c; } });
+  const [branch1, branch2] = stream.tee();
+
+  const error = new Error();
+  error.name = 'distinctive';
+
+  // Ensure neither branch is waiting in ReadableStreamDefaultReaderRead().
+  controller.enqueue();
+  controller.enqueue();
+
+  return delay(0).then(() => {
+    // This error will have to be detected via [[closedPromise]].
+    controller.error(error);
+
+    const reader1 = branch1.getReader();
+    const reader2 = branch2.getReader();
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, reader1.closed, 'reader1.closed should reject'),
+      promise_rejects_exactly(t, error, reader2.closed, 'reader2.closed should reject')
+    ]);
+  });
+
+}, 'ReadableStream teeing: erroring a teed stream should error both branches');
+
+promise_test(() => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const branches = rs.tee();
+  const reader1 = branches[0].getReader();
+  const reader2 = branches[1].getReader();
+
+  const promise = Promise.all([reader1.closed, reader2.closed]);
+
+  controller.close();
+  return promise;
+
+}, 'ReadableStream teeing: closing the original should immediately close the branches');
+
+promise_test(t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const branches = rs.tee();
+  const reader1 = branches[0].getReader();
+  const reader2 = branches[1].getReader();
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+  controller.error(theError);
+  return promise;
+
+}, 'ReadableStream teeing: erroring the original should immediately error the branches');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+  const cancelPromise = reader2.cancel();
+
+  controller.enqueue('a');
+
+  const read1 = await reader1.read();
+  assert_object_equals(read1, { value: 'a', done: false }, 'first read() from branch1 should fulfill with the chunk');
+
+  controller.close();
+
+  const read2 = await reader1.read();
+  assert_object_equals(read2, { value: undefined, done: true }, 'second read() from branch1 should be done');
+
+  await Promise.all([
+    reader1.closed,
+    cancelPromise
+  ]);
+
+}, 'ReadableStream teeing: canceling branch1 should finish when branch2 reads until end of stream');
+
+promise_test(async t => {
+
+  let controller;
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+  const cancelPromise = reader2.cancel();
+
+  controller.error(theError);
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read()),
+    cancelPromise
+  ]);
+
+}, 'ReadableStream teeing: canceling branch1 should finish when original stream errors');
+
+promise_test(async () => {
+
+  const rs = new ReadableStream({});
+
+  const [branch1, branch2] = rs.tee();
+
+  const cancel1 = branch1.cancel();
+  await flushAsyncEvents();
+  const cancel2 = branch2.cancel();
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing: canceling both branches in sequence with delay');
+
+promise_test(async t => {
+
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    cancel() {
+      throw theError;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+
+  const cancel1 = branch1.cancel();
+  await flushAsyncEvents();
+  const cancel2 = branch2.cancel();
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, cancel1),
+    promise_rejects_exactly(t, theError, cancel2)
+  ]);
+
+}, 'ReadableStream teeing: failing to cancel when canceling both branches in sequence with delay');
+
+test(t => {
+
+  // Copy original global.
+  const oldReadableStream = ReadableStream;
+  const getReader = ReadableStream.prototype.getReader;
+
+  const origRS = new ReadableStream();
+
+  // Replace the global ReadableStream constructor with one that doesn't work.
+  ReadableStream = function() {
+    throw new Error('global ReadableStream constructor called');
+  };
+  t.add_cleanup(() => {
+    ReadableStream = oldReadableStream;
+  });
+
+  // This will probably fail if the global ReadableStream constructor was used.
+  const [rs1, rs2] = origRS.tee();
+
+  // These will definitely fail if the global ReadableStream constructor was used.
+  assert_not_equals(getReader.call(rs1), undefined, 'getReader should work on rs1');
+  assert_not_equals(getReader.call(rs2), undefined, 'getReader should work on rs2');
+
+}, 'ReadableStreamTee should not use a modified ReadableStream constructor from the global object');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({}, { highWaterMark: 0 });
+
+  // Create two branches, each with a HWM of 1. This should result in one
+  // chunk being pulled, not two.
+  rs.tee();
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(rs.events, ['pull'], 'pull should only be called once');
+  });
+
+}, 'ReadableStreamTee should not pull more chunks than can fit in the branch queue');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    pull(controller) {
+      controller.enqueue('a');
+    }
+  }, { highWaterMark: 0 });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+  return Promise.all([reader1.read(), reader2.read()])
+      .then(() => {
+    assert_array_equals(rs.events, ['pull', 'pull'], 'pull should be called twice');
+  });
+
+}, 'ReadableStreamTee should only pull enough to fill the emptiest queue');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({}, { highWaterMark: 0 });
+  const theError = { name: 'boo!' };
+
+  rs.controller.error(theError);
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(rs.events, [], 'pull should not be called');
+
+    return Promise.all([
+      promise_rejects_exactly(t, theError, reader1.closed),
+      promise_rejects_exactly(t, theError, reader2.closed)
+    ]);
+  });
+
+}, 'ReadableStreamTee should not pull when original is already errored');
+
+for (const branch of [1, 2]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream({}, { highWaterMark: 0 });
+    const theError = { name: 'boo!' };
+
+    const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+
+    return flushAsyncEvents().then(() => {
+      assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+      rs.controller.enqueue('a');
+
+      const reader = (branch === 1) ? reader1 : reader2;
+      return reader.read();
+    }).then(() => flushAsyncEvents()).then(() => {
+      assert_array_equals(rs.events, ['pull', 'pull'], 'pull should be called twice');
+
+      rs.controller.error(theError);
+
+      return Promise.all([
+        promise_rejects_exactly(t, theError, reader1.closed),
+        promise_rejects_exactly(t, theError, reader2.closed)
+      ]);
+    }).then(() => flushAsyncEvents()).then(() => {
+      assert_array_equals(rs.events, ['pull', 'pull'], 'pull should be called twice');
+    });
+
+  }, `ReadableStreamTee stops pulling when original stream errors while branch ${branch} is reading`);
+}
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({}, { highWaterMark: 0 });
+  const theError = { name: 'boo!' };
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+    rs.controller.enqueue('a');
+
+    return Promise.all([reader1.read(), reader2.read()]);
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(rs.events, ['pull', 'pull'], 'pull should be called twice');
+
+    rs.controller.error(theError);
+
+    return Promise.all([
+      promise_rejects_exactly(t, theError, reader1.closed),
+      promise_rejects_exactly(t, theError, reader2.closed)
+    ]);
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(rs.events, ['pull', 'pull'], 'pull should be called twice');
+  });
+
+}, 'ReadableStreamTee stops pulling when original stream errors while both branches are reading');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream();
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+  const branch1Reads = [reader1.read(), reader1.read()];
+  const branch2Reads = [reader2.read(), reader2.read()];
+
+  await flushAsyncEvents();
+  rs.controller.enqueue('a');
+  rs.controller.close();
+
+  assert_object_equals(await branch1Reads[0], { value: 'a', done: false }, 'first chunk from branch1 should be correct');
+  assert_object_equals(await branch2Reads[0], { value: 'a', done: false }, 'first chunk from branch2 should be correct');
+
+  assert_object_equals(await branch1Reads[1], { value: undefined, done: true }, 'second read() from branch1 should be done');
+  assert_object_equals(await branch2Reads[1], { value: undefined, done: true }, 'second read() from branch2 should be done');
+
+}, 'ReadableStream teeing: enqueue() and close() while both branches are pulling');
diff --git a/testing/web-platform/tests/streams/readable-streams/templated.any.js b/testing/web-platform/tests/streams/readable-streams/templated.any.js
new file mode 100644
index 0000000000..ecae3f4d8b
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/templated.any.js
@@ -0,0 +1,143 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-test-templates.js
+'use strict';
+
+// Run the readable stream test templates against readable streams created directly using the constructor
+
+const theError = { name: 'boo!' };
+const chunks = ['a', 'b'];
+
+templatedRSEmpty('ReadableStream (empty)', () => {
+  return new ReadableStream();
+});
+
+templatedRSEmptyReader('ReadableStream (empty) reader', () => {
+  return streamAndDefaultReader(new ReadableStream());
+});
+
+templatedRSClosed('ReadableStream (closed via call in start)', () => {
+  return new ReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+});
+
+templatedRSClosedReader('ReadableStream reader (closed before getting reader)', () => {
+  let controller;
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  controller.close();
+  const result = streamAndDefaultReader(stream);
+  return result;
+});
+
+templatedRSClosedReader('ReadableStream reader (closed after getting reader)', () => {
+  let controller;
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const result = streamAndDefaultReader(stream);
+  controller.close();
+  return result;
+});
+
+templatedRSClosed('ReadableStream (closed via cancel)', () => {
+  const stream = new ReadableStream();
+  stream.cancel();
+  return stream;
+});
+
+templatedRSClosedReader('ReadableStream reader (closed via cancel after getting reader)', () => {
+  const stream = new ReadableStream();
+  const result = streamAndDefaultReader(stream);
+  result.reader.cancel();
+  return result;
+});
+
+templatedRSErrored('ReadableStream (errored via call in start)', () => {
+  return new ReadableStream({
+    start(c) {
+      c.error(theError);
+    }
+  });
+}, theError);
+
+templatedRSErroredSyncOnly('ReadableStream (errored via call in start)', () => {
+  return new ReadableStream({
+    start(c) {
+      c.error(theError);
+    }
+  });
+}, theError);
+
+templatedRSErrored('ReadableStream (errored via returning a rejected promise in start)', () => {
+  return new ReadableStream({
+    start() {
+      return Promise.reject(theError);
+    }
+  });
+}, theError);
+
+templatedRSErroredReader('ReadableStream (errored via returning a rejected promise in start) reader', () => {
+  return streamAndDefaultReader(new ReadableStream({
+    start() {
+      return Promise.reject(theError);
+    }
+  }));
+}, theError);
+
+templatedRSErroredReader('ReadableStream reader (errored before getting reader)', () => {
+  let controller;
+  const stream = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  controller.error(theError);
+  return streamAndDefaultReader(stream);
+}, theError);
+
+templatedRSErroredReader('ReadableStream reader (errored after getting reader)', () => {
+  let controller;
+  const result = streamAndDefaultReader(new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }));
+  controller.error(theError);
+  return result;
+}, theError);
+
+templatedRSTwoChunksOpenReader('ReadableStream (two chunks enqueued, still open) reader', () => {
+  return streamAndDefaultReader(new ReadableStream({
+    start(c) {
+      c.enqueue(chunks[0]);
+      c.enqueue(chunks[1]);
+    }
+  }));
+}, chunks);
+
+templatedRSTwoChunksClosedReader('ReadableStream (two chunks enqueued, then closed) reader', () => {
+  let doClose;
+  const stream = new ReadableStream({
+    start(c) {
+      c.enqueue(chunks[0]);
+      c.enqueue(chunks[1]);
+      doClose = c.close.bind(c);
+    }
+  });
+  const result = streamAndDefaultReader(stream);
+  doClose();
+  return result;
+}, chunks);
+
+function streamAndDefaultReader(stream) {
+  return { stream, reader: stream.getReader() };
+}
diff --git a/testing/web-platform/tests/streams/resources/recording-streams.js b/testing/web-platform/tests/streams/resources/recording-streams.js
new file mode 100644
index 0000000000..661fe512f5
--- /dev/null
+++ b/testing/web-platform/tests/streams/resources/recording-streams.js
@@ -0,0 +1,131 @@
+'use strict';
+
+self.recordingReadableStream = (extras = {}, strategy) => {
+  let controllerToCopyOver;
+  const stream = new ReadableStream({
+    type: extras.type,
+    start(controller) {
+      controllerToCopyOver = controller;
+
+      if (extras.start) {
+        return extras.start(controller);
+      }
+
+      return undefined;
+    },
+    pull(controller) {
+      stream.events.push('pull');
+
+      if (extras.pull) {
+        return extras.pull(controller);
+      }
+
+      return undefined;
+    },
+    cancel(reason) {
+      stream.events.push('cancel', reason);
+      stream.eventsWithoutPulls.push('cancel', reason);
+
+      if (extras.cancel) {
+        return extras.cancel(reason);
+      }
+
+      return undefined;
+    }
+  }, strategy);
+
+  stream.controller = controllerToCopyOver;
+  stream.events = [];
+  stream.eventsWithoutPulls = [];
+
+  return stream;
+};
+
+self.recordingWritableStream = (extras = {}, strategy) => {
+  let controllerToCopyOver;
+  const stream = new WritableStream({
+    start(controller) {
+      controllerToCopyOver = controller;
+
+      if (extras.start) {
+        return extras.start(controller);
+      }
+
+      return undefined;
+    },
+    write(chunk, controller) {
+      stream.events.push('write', chunk);
+
+      if (extras.write) {
+        return extras.write(chunk, controller);
+      }
+
+      return undefined;
+    },
+    close() {
+      stream.events.push('close');
+
+      if (extras.close) {
+        return extras.close();
+      }
+
+      return undefined;
+    },
+    abort(e) {
+      stream.events.push('abort', e);
+
+      if (extras.abort) {
+        return extras.abort(e);
+      }
+
+      return undefined;
+    }
+  }, strategy);
+
+  stream.controller = controllerToCopyOver;
+  stream.events = [];
+
+  return stream;
+};
+
+self.recordingTransformStream = (extras = {}, writableStrategy, readableStrategy) => {
+  let controllerToCopyOver;
+  const stream = new TransformStream({
+    start(controller) {
+      controllerToCopyOver = controller;
+
+      if (extras.start) {
+        return extras.start(controller);
+      }
+
+      return undefined;
+    },
+
+    transform(chunk, controller) {
+      stream.events.push('transform', chunk);
+
+      if (extras.transform) {
+        return extras.transform(chunk, controller);
+      }
+
+      controller.enqueue(chunk);
+
+      return undefined;
+    },
+
+    flush(controller) {
+      stream.events.push('flush');
+
+      if (extras.flush) {
+        return extras.flush(controller);
+      }
+
+      return undefined;
+    }
+  }, writableStrategy, readableStrategy);
+
+  stream.controller = controllerToCopyOver;
+  stream.events = [];
+
+  return stream;
+};
diff --git a/testing/web-platform/tests/streams/resources/rs-test-templates.js b/testing/web-platform/tests/streams/resources/rs-test-templates.js
new file mode 100644
index 0000000000..25751c477f
--- /dev/null
+++ b/testing/web-platform/tests/streams/resources/rs-test-templates.js
@@ -0,0 +1,721 @@
+'use strict';
+
+// These tests can be run against any readable stream produced by the web platform that meets the given descriptions.
+// For readable stream tests, the factory should return the stream. For reader tests, the factory should return a
+// { stream, reader } object. (You can use this to vary the time at which you acquire a reader.)
+
+self.templatedRSEmpty = (label, factory) => {
+  test(() => {}, 'Running templatedRSEmpty with ' + label);
+
+  test(() => {
+
+    const rs = factory();
+
+    assert_equals(typeof rs.locked, 'boolean', 'has a boolean locked getter');
+    assert_equals(typeof rs.cancel, 'function', 'has a cancel method');
+    assert_equals(typeof rs.getReader, 'function', 'has a getReader method');
+    assert_equals(typeof rs.pipeThrough, 'function', 'has a pipeThrough method');
+    assert_equals(typeof rs.pipeTo, 'function', 'has a pipeTo method');
+    assert_equals(typeof rs.tee, 'function', 'has a tee method');
+
+  }, label + ': instances have the correct methods and properties');
+
+  test(() => {
+    const rs = factory();
+
+    assert_throws_js(TypeError, () => rs.getReader({ mode: '' }), 'empty string mode should throw');
+    assert_throws_js(TypeError, () => rs.getReader({ mode: null }), 'null mode should throw');
+    assert_throws_js(TypeError, () => rs.getReader({ mode: 'asdf' }), 'asdf mode should throw');
+    assert_throws_js(TypeError, () => rs.getReader(5), '5 should throw');
+
+    // Should not throw
+    rs.getReader(null);
+
+  }, label + ': calling getReader with invalid arguments should throw appropriate errors');
+};
+
+self.templatedRSClosed = (label, factory) => {
+  test(() => {}, 'Running templatedRSClosed with ' + label);
+
+  promise_test(() => {
+
+    const rs = factory();
+    const cancelPromise1 = rs.cancel();
+    const cancelPromise2 = rs.cancel();
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+
+    return Promise.all([
+      cancelPromise1.then(v => assert_equals(v, undefined, 'first cancel() call should fulfill with undefined')),
+      cancelPromise2.then(v => assert_equals(v, undefined, 'second cancel() call should fulfill with undefined'))
+    ]);
+
+  }, label + ': cancel() should return a distinct fulfilled promise each time');
+
+  test(() => {
+
+    const rs = factory();
+    assert_false(rs.locked, 'locked getter should return false');
+
+  }, label + ': locked should be false');
+
+  test(() => {
+
+    const rs = factory();
+    rs.getReader(); // getReader() should not throw.
+
+  }, label + ': getReader() should be OK');
+
+  test(() => {
+
+    const rs = factory();
+
+    const reader = rs.getReader();
+    reader.releaseLock();
+
+    const reader2 = rs.getReader(); // Getting a second reader should not throw.
+    reader2.releaseLock();
+
+    rs.getReader(); // Getting a third reader should not throw.
+
+  }, label + ': should be able to acquire multiple readers if they are released in succession');
+
+  test(() => {
+
+    const rs = factory();
+
+    rs.getReader();
+
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a second reader should throw');
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a third reader should throw');
+
+  }, label + ': should not be able to acquire a second reader if we don\'t release the first one');
+};
+
+self.templatedRSErrored = (label, factory, error) => {
+  test(() => {}, 'Running templatedRSErrored with ' + label);
+
+  promise_test(t => {
+
+    const rs = factory();
+    const reader = rs.getReader();
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, reader.closed),
+      promise_rejects_exactly(t, error, reader.read())
+    ]);
+
+  }, label + ': getReader() should return a reader that acts errored');
+
+  promise_test(t => {
+
+    const rs = factory();
+    const reader = rs.getReader();
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, reader.read()),
+      promise_rejects_exactly(t, error, reader.read()),
+      promise_rejects_exactly(t, error, reader.closed)
+    ]);
+
+  }, label + ': read() twice should give the error each time');
+
+  test(() => {
+    const rs = factory();
+
+    assert_false(rs.locked, 'locked getter should return false');
+  }, label + ': locked should be false');
+};
+
+self.templatedRSErroredSyncOnly = (label, factory, error) => {
+  test(() => {}, 'Running templatedRSErroredSyncOnly with ' + label);
+
+  promise_test(t => {
+
+    const rs = factory();
+    rs.getReader().releaseLock();
+    const reader = rs.getReader(); // Calling getReader() twice does not throw (the stream is not locked).
+
+    return promise_rejects_exactly(t, error, reader.closed);
+
+  }, label + ': should be able to obtain a second reader, with the correct closed promise');
+
+  test(() => {
+
+    const rs = factory();
+    rs.getReader();
+
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a second reader should throw a TypeError');
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a third reader should throw a TypeError');
+
+  }, label + ': should not be able to obtain additional readers if we don\'t release the first lock');
+
+  promise_test(t => {
+
+    const rs = factory();
+    const cancelPromise1 = rs.cancel();
+    const cancelPromise2 = rs.cancel();
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, cancelPromise1),
+      promise_rejects_exactly(t, error, cancelPromise2)
+    ]);
+
+  }, label + ': cancel() should return a distinct rejected promise each time');
+
+  promise_test(t => {
+
+    const rs = factory();
+    const reader = rs.getReader();
+    const cancelPromise1 = reader.cancel();
+    const cancelPromise2 = reader.cancel();
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, cancelPromise1),
+      promise_rejects_exactly(t, error, cancelPromise2)
+    ]);
+
+  }, label + ': reader cancel() should return a distinct rejected promise each time');
+};
+
+self.templatedRSEmptyReader = (label, factory) => {
+  test(() => {}, 'Running templatedRSEmptyReader with ' + label);
+
+  test(() => {
+
+    const reader = factory().reader;
+
+    assert_true('closed' in reader, 'has a closed property');
+    assert_equals(typeof reader.closed.then, 'function', 'closed property is thenable');
+
+    assert_equals(typeof reader.cancel, 'function', 'has a cancel method');
+    assert_equals(typeof reader.read, 'function', 'has a read method');
+    assert_equals(typeof reader.releaseLock, 'function', 'has a releaseLock method');
+
+  }, label + ': instances have the correct methods and properties');
+
+  test(() => {
+
+    const stream = factory().stream;
+
+    assert_true(stream.locked, 'locked getter should return true');
+
+  }, label + ': locked should be true');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    reader.read().then(
+      t.unreached_func('read() should not fulfill'),
+      t.unreached_func('read() should not reject')
+    );
+
+    return delay(500);
+
+  }, label + ': read() should never settle');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    reader.read().then(
+      t.unreached_func('read() should not fulfill'),
+      t.unreached_func('read() should not reject')
+    );
+
+    reader.read().then(
+      t.unreached_func('read() should not fulfill'),
+      t.unreached_func('read() should not reject')
+    );
+
+    return delay(500);
+
+  }, label + ': two read()s should both never settle');
+
+  test(() => {
+
+    const reader = factory().reader;
+    assert_not_equals(reader.read(), reader.read(), 'the promises returned should be distinct');
+
+  }, label + ': read() should return distinct promises each time');
+
+  test(() => {
+
+    const stream = factory().stream;
+    assert_throws_js(TypeError, () => stream.getReader(), 'stream.getReader() should throw a TypeError');
+
+  }, label + ': getReader() again on the stream should fail');
+
+  promise_test(async t => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    const read1 = reader.read();
+    const read2 = reader.read();
+    const closed = reader.closed;
+
+    reader.releaseLock();
+
+    assert_false(stream.locked, 'the stream should be unlocked');
+
+    await Promise.all([
+      promise_rejects_js(t, TypeError, read1, 'first read should reject'),
+      promise_rejects_js(t, TypeError, read2, 'second read should reject'),
+      promise_rejects_js(t, TypeError, closed, 'closed should reject')
+    ]);
+
+  }, label + ': releasing the lock should reject all pending read requests');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    reader.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, reader.read()),
+      promise_rejects_js(t, TypeError, reader.read())
+    ]);
+
+  }, label + ': releasing the lock should cause further read() calls to reject with a TypeError');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    const closedBefore = reader.closed;
+    reader.releaseLock();
+    const closedAfter = reader.closed;
+
+    assert_equals(closedBefore, closedAfter, 'the closed promise should not change identity');
+
+    return promise_rejects_js(t, TypeError, closedBefore);
+
+  }, label + ': releasing the lock should cause closed calls to reject with a TypeError');
+
+  test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    reader.releaseLock();
+    assert_false(stream.locked, 'locked getter should return false');
+
+  }, label + ': releasing the lock should cause locked to become false');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+    reader.cancel();
+
+    return reader.read().then(r => {
+      assert_object_equals(r, { value: undefined, done: true }, 'read()ing from the reader should give a done result');
+    });
+
+  }, label + ': canceling via the reader should cause the reader to act closed');
+
+  promise_test(t => {
+
+    const stream = factory().stream;
+    return promise_rejects_js(t, TypeError, stream.cancel());
+
+  }, label + ': canceling via the stream should fail');
+};
+
+self.templatedRSClosedReader = (label, factory) => {
+  test(() => {}, 'Running templatedRSClosedReader with ' + label);
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(v => {
+      assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+    });
+
+  }, label + ': read() should fulfill with { value: undefined, done: true }');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return Promise.all([
+      reader.read().then(v => {
+        assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+      }),
+      reader.read().then(v => {
+        assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+      })
+    ]);
+
+  }, label + ': read() multiple times should fulfill with { value: undefined, done: true }');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(() => reader.read()).then(v => {
+      assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+    });
+
+  }, label + ': read() should work when used within another read() fulfill callback');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.closed.then(v => assert_equals(v, undefined, 'reader closed should fulfill with undefined'));
+
+  }, label + ': closed should fulfill with undefined');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    const closedBefore = reader.closed;
+    reader.releaseLock();
+    const closedAfter = reader.closed;
+
+    assert_not_equals(closedBefore, closedAfter, 'the closed promise should change identity');
+
+    return Promise.all([
+      closedBefore.then(v => assert_equals(v, undefined, 'reader.closed acquired before release should fulfill')),
+      promise_rejects_js(t, TypeError, closedAfter)
+    ]);
+
+  }, label + ': releasing the lock should cause closed to reject and change identity');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+    const cancelPromise1 = reader.cancel();
+    const cancelPromise2 = reader.cancel();
+    const closedReaderPromise = reader.closed;
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+    assert_not_equals(cancelPromise1, closedReaderPromise, 'cancel() promise 1 should be distinct from reader.closed');
+    assert_not_equals(cancelPromise2, closedReaderPromise, 'cancel() promise 2 should be distinct from reader.closed');
+
+    return Promise.all([
+      cancelPromise1.then(v => assert_equals(v, undefined, 'first cancel() should fulfill with undefined')),
+      cancelPromise2.then(v => assert_equals(v, undefined, 'second cancel() should fulfill with undefined'))
+    ]);
+
+  }, label + ': cancel() should return a distinct fulfilled promise each time');
+};
+
+self.templatedRSErroredReader = (label, factory, error) => {
+  test(() => {}, 'Running templatedRSErroredReader with ' + label);
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    return promise_rejects_exactly(t, error, reader.closed);
+
+  }, label + ': closed should reject with the error');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    const closedBefore = reader.closed;
+
+    return promise_rejects_exactly(t, error, closedBefore).then(() => {
+      reader.releaseLock();
+
+      const closedAfter = reader.closed;
+      assert_not_equals(closedBefore, closedAfter, 'the closed promise should change identity');
+
+      return promise_rejects_js(t, TypeError, closedAfter);
+    });
+
+  }, label + ': releasing the lock should cause closed to reject and change identity');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    return promise_rejects_exactly(t, error, reader.read());
+
+  }, label + ': read() should reject with the error');
+};
+
+self.templatedRSTwoChunksOpenReader = (label, factory, chunks) => {
+  test(() => {}, 'Running templatedRSTwoChunksOpenReader with ' + label);
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return Promise.all([
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+      }),
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[1], done: false }, 'second result should be correct');
+      })
+    ]);
+
+  }, label + ': calling read() twice without waiting will eventually give both chunks (sequential)');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(r => {
+      assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+
+      return reader.read().then(r2 => {
+        assert_object_equals(r2, { value: chunks[1], done: false }, 'second result should be correct');
+      });
+    });
+
+  }, label + ': calling read() twice without waiting will eventually give both chunks (nested)');
+
+  test(() => {
+
+    const reader = factory().reader;
+    assert_not_equals(reader.read(), reader.read(), 'the promises returned should be distinct');
+
+  }, label + ': read() should return distinct promises each time');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    const promise1 = reader.closed.then(v => {
+      assert_equals(v, undefined, 'reader closed should fulfill with undefined');
+    });
+
+    const promise2 = reader.read().then(r => {
+      assert_object_equals(r, { value: chunks[0], done: false },
+                           'promise returned before cancellation should fulfill with a chunk');
+    });
+
+    reader.cancel();
+
+    const promise3 = reader.read().then(r => {
+      assert_object_equals(r, { value: undefined, done: true },
+                           'promise returned after cancellation should fulfill with an end-of-stream signal');
+    });
+
+    return Promise.all([promise1, promise2, promise3]);
+
+  }, label + ': cancel() after a read() should still give that single read result');
+};
+
+self.templatedRSTwoChunksClosedReader = function (label, factory, chunks) {
+  test(() => {}, 'Running templatedRSTwoChunksClosedReader with ' + label);
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return Promise.all([
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+      }),
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[1], done: false }, 'second result should be correct');
+      }),
+      reader.read().then(r => {
+        assert_object_equals(r, { value: undefined, done: true }, 'third result should be correct');
+      })
+    ]);
+
+  }, label + ': third read(), without waiting, should give { value: undefined, done: true } (sequential)');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(r => {
+      assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+
+      return reader.read().then(r2 => {
+        assert_object_equals(r2, { value: chunks[1], done: false }, 'second result should be correct');
+
+        return reader.read().then(r3 => {
+          assert_object_equals(r3, { value: undefined, done: true }, 'third result should be correct');
+        });
+      });
+    });
+
+  }, label + ': third read(), without waiting, should give { value: undefined, done: true } (nested)');
+
+  promise_test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    assert_true(stream.locked, 'stream should start locked');
+
+    const promise = reader.closed.then(v => {
+      assert_equals(v, undefined, 'reader closed should fulfill with undefined');
+      assert_true(stream.locked, 'stream should remain locked');
+    });
+
+    reader.read();
+    reader.read();
+
+    return promise;
+
+  }, label +
+     ': draining the stream via read() should cause the reader closed promise to fulfill, but locked stays true');
+
+  promise_test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    const promise = reader.closed.then(() => {
+      assert_true(stream.locked, 'the stream should start locked');
+      reader.releaseLock(); // Releasing the lock after reader closed should not throw.
+      assert_false(stream.locked, 'the stream should end unlocked');
+    });
+
+    reader.read();
+    reader.read();
+
+    return promise;
+
+  }, label + ': releasing the lock after the stream is closed should cause locked to become false');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    reader.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, reader.read()),
+      promise_rejects_js(t, TypeError, reader.read()),
+      promise_rejects_js(t, TypeError, reader.read())
+    ]);
+
+  }, label + ': releasing the lock should cause further read() calls to reject with a TypeError');
+
+  promise_test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    const readerClosed = reader.closed;
+
+    assert_equals(reader.closed, readerClosed, 'accessing reader.closed twice in succession gives the same value');
+
+    const promise = reader.read().then(() => {
+      assert_equals(reader.closed, readerClosed, 'reader.closed is the same after read() fulfills');
+
+      reader.releaseLock();
+
+      assert_equals(reader.closed, readerClosed, 'reader.closed is the same after releasing the lock');
+
+      const newReader = stream.getReader();
+      return newReader.read();
+    });
+
+    assert_equals(reader.closed, readerClosed, 'reader.closed is the same after calling read()');
+
+    return promise;
+
+  }, label + ': reader\'s closed property always returns the same promise');
+};
+
+self.templatedRSTeeCancel = (label, factory) => {
+  test(() => {}, `Running templatedRSTeeCancel with ${label}`);
+
+  promise_test(async () => {
+
+    const reason1 = new Error('We\'re wanted men.');
+    const reason2 = new Error('I have the death sentence on twelve systems.');
+
+    let resolve;
+    const promise = new Promise(r => resolve = r);
+    const rs = factory({
+      cancel(reason) {
+        assert_array_equals(reason, [reason1, reason2],
+          'the cancel reason should be an array containing those from the branches');
+        resolve();
+      }
+    });
+
+    const [branch1, branch2] = rs.tee();
+    await Promise.all([
+      branch1.cancel(reason1),
+      branch2.cancel(reason2),
+      promise
+    ]);
+
+  }, `${label}: canceling both branches should aggregate the cancel reasons into an array`);
+
+  promise_test(async () => {
+
+    const reason1 = new Error('This little one\'s not worth the effort.');
+    const reason2 = new Error('Come, let me get you something.');
+
+    let resolve;
+    const promise = new Promise(r => resolve = r);
+    const rs = factory({
+      cancel(reason) {
+        assert_array_equals(reason, [reason1, reason2],
+          'the cancel reason should be an array containing those from the branches');
+        resolve();
+      }
+    });
+
+    const [branch1, branch2] = rs.tee();
+    await Promise.all([
+      branch2.cancel(reason2),
+      branch1.cancel(reason1),
+      promise
+    ]);
+
+  }, `${label}: canceling both branches in reverse order should aggregate the cancel reasons into an array`);
+
+  promise_test(async t => {
+
+    const theError = { name: 'I\'ll be careful.' };
+    const rs = factory({
+      cancel() {
+        throw theError;
+      }
+    });
+
+    const [branch1, branch2] = rs.tee();
+    await Promise.all([
+      promise_rejects_exactly(t, theError, branch1.cancel()),
+      promise_rejects_exactly(t, theError, branch2.cancel())
+    ]);
+
+  }, `${label}: failing to cancel the original stream should cause cancel() to reject on branches`);
+
+  promise_test(async t => {
+
+    const theError = { name: 'You just watch yourself!' };
+    let controller;
+    const stream = factory({
+      start(c) {
+        controller = c;
+      }
+    });
+
+    const [branch1, branch2] = stream.tee();
+    controller.error(theError);
+
+    await Promise.all([
+      promise_rejects_exactly(t, theError, branch1.cancel()),
+      promise_rejects_exactly(t, theError, branch2.cancel())
+    ]);
+
+  }, `${label}: erroring a teed stream should properly handle canceled branches`);
+
+};
diff --git a/testing/web-platform/tests/streams/resources/rs-utils.js b/testing/web-platform/tests/streams/resources/rs-utils.js
new file mode 100644
index 0000000000..f1a014275a
--- /dev/null
+++ b/testing/web-platform/tests/streams/resources/rs-utils.js
@@ -0,0 +1,197 @@
+'use strict';
+(function () {
+
+  class RandomPushSource {
+    constructor(toPush) {
+      this.pushed = 0;
+      this.toPush = toPush;
+      this.started = false;
+      this.paused = false;
+      this.closed = false;
+
+      this._intervalHandle = null;
+    }
+
+    readStart() {
+      if (this.closed) {
+        return;
+      }
+
+      if (!this.started) {
+        this._intervalHandle = setInterval(writeChunk, 2);
+        this.started = true;
+      }
+
+      if (this.paused) {
+        this._intervalHandle = setInterval(writeChunk, 2);
+        this.paused = false;
+      }
+
+      const source = this;
+      function writeChunk() {
+        if (source.paused) {
+          return;
+        }
+
+        source.pushed++;
+
+        if (source.toPush > 0 && source.pushed > source.toPush) {
+          if (source._intervalHandle) {
+            clearInterval(source._intervalHandle);
+            source._intervalHandle = undefined;
+          }
+          source.closed = true;
+          source.onend();
+        } else {
+          source.ondata(randomChunk(128));
+        }
+      }
+    }
+
+    readStop() {
+      if (this.paused) {
+        return;
+      }
+
+      if (this.started) {
+        this.paused = true;
+        clearInterval(this._intervalHandle);
+        this._intervalHandle = undefined;
+      } else {
+        throw new Error('Can\'t pause reading an unstarted source.');
+      }
+    }
+  }
+
+  function randomChunk(size) {
+    let chunk = '';
+
+    for (let i = 0; i < size; ++i) {
+      // Add a random character from the basic printable ASCII set.
+      chunk += String.fromCharCode(Math.round(Math.random() * 84) + 32);
+    }
+
+    return chunk;
+  }
+
+  function readableStreamToArray(readable, reader) {
+    if (reader === undefined) {
+      reader = readable.getReader();
+    }
+
+    const chunks = [];
+
+    return pump();
+
+    function pump() {
+      return reader.read().then(result => {
+        if (result.done) {
+          return chunks;
+        }
+
+        chunks.push(result.value);
+        return pump();
+      });
+    }
+  }
+
+  class SequentialPullSource {
+    constructor(limit, options) {
+      const async = options && options.async;
+
+      this.current = 0;
+      this.limit = limit;
+      this.opened = false;
+      this.closed = false;
+
+      this._exec = f => f();
+      if (async) {
+        this._exec = f => step_timeout(f, 0);
+      }
+    }
+
+    open(cb) {
+      this._exec(() => {
+        this.opened = true;
+        cb();
+      });
+    }
+
+    read(cb) {
+      this._exec(() => {
+        if (++this.current <= this.limit) {
+          cb(null, false, this.current);
+        } else {
+          cb(null, true, null);
+        }
+      });
+    }
+
+    close(cb) {
+      this._exec(() => {
+        this.closed = true;
+        cb();
+      });
+    }
+  }
+
+  function sequentialReadableStream(limit, options) {
+    const sequentialSource = new SequentialPullSource(limit, options);
+
+    const stream = new ReadableStream({
+      start() {
+        return new Promise((resolve, reject) => {
+          sequentialSource.open(err => {
+            if (err) {
+              reject(err);
+            }
+            resolve();
+          });
+        });
+      },
+
+      pull(c) {
+        return new Promise((resolve, reject) => {
+          sequentialSource.read((err, done, chunk) => {
+            if (err) {
+              reject(err);
+            } else if (done) {
+              sequentialSource.close(err2 => {
+                if (err2) {
+                  reject(err2);
+                }
+                c.close();
+                resolve();
+              });
+            } else {
+              c.enqueue(chunk);
+              resolve();
+            }
+          });
+        });
+      }
+    });
+
+    stream.source = sequentialSource;
+
+    return stream;
+  }
+
+  function transferArrayBufferView(view) {
+    const noopByteStream = new ReadableStream({
+      type: 'bytes',
+      pull(c) {
+        c.byobRequest.respond(c.byobRequest.view.byteLength);
+        c.close();
+      }
+    });
+    const reader = noopByteStream.getReader({ mode: 'byob' });
+    return reader.read(view).then((result) => result.value);
+  }
+
+  self.RandomPushSource = RandomPushSource;
+  self.readableStreamToArray = readableStreamToArray;
+  self.sequentialReadableStream = sequentialReadableStream;
+  self.transferArrayBufferView = transferArrayBufferView;
+
+}());
diff --git a/testing/web-platform/tests/streams/resources/test-utils.js b/testing/web-platform/tests/streams/resources/test-utils.js
new file mode 100644
index 0000000000..5ff8fc8cec
--- /dev/null
+++ b/testing/web-platform/tests/streams/resources/test-utils.js
@@ -0,0 +1,74 @@
+'use strict';
+
+self.getterRejects = (t, obj, getterName, target) => {
+  const getter = Object.getOwnPropertyDescriptor(obj, getterName).get;
+
+  return promise_rejects_js(t, TypeError, getter.call(target), getterName + ' should reject with a TypeError');
+};
+
+self.getterRejectsForAll = (t, obj, getterName, targets) => {
+  return Promise.all(targets.map(target => self.getterRejects(t, obj, getterName, target)));
+};
+
+self.methodRejects = (t, obj, methodName, target, args) => {
+  const method = obj[methodName];
+
+  return promise_rejects_js(t, TypeError, method.apply(target, args),
+                         methodName + ' should reject with a TypeError');
+};
+
+self.methodRejectsForAll = (t, obj, methodName, targets, args) => {
+  return Promise.all(targets.map(target => self.methodRejects(t, obj, methodName, target, args)));
+};
+
+self.getterThrows = (obj, getterName, target) => {
+  const getter = Object.getOwnPropertyDescriptor(obj, getterName).get;
+
+  assert_throws_js(TypeError, () => getter.call(target), getterName + ' should throw a TypeError');
+};
+
+self.getterThrowsForAll = (obj, getterName, targets) => {
+  targets.forEach(target => self.getterThrows(obj, getterName, target));
+};
+
+self.methodThrows = (obj, methodName, target, args) => {
+  const method = obj[methodName];
+  assert_equals(typeof method, 'function', methodName + ' should exist');
+
+  assert_throws_js(TypeError, () => method.apply(target, args), methodName + ' should throw a TypeError');
+};
+
+self.methodThrowsForAll = (obj, methodName, targets, args) => {
+  targets.forEach(target => self.methodThrows(obj, methodName, target, args));
+};
+
+self.constructorThrowsForAll = (constructor, firstArgs) => {
+  firstArgs.forEach(firstArg => assert_throws_js(TypeError, () => new constructor(firstArg),
+                                                 'constructor should throw a TypeError'));
+};
+
+self.delay = ms => new Promise(resolve => step_timeout(resolve, ms));
+
+// For tests which verify that the implementation doesn't do something it shouldn't, it's better not to use a
+// timeout. Instead, assume that any reasonable implementation is going to finish work after 2 times around the event
+// loop, and use flushAsyncEvents().then(() => assert_array_equals(...));
+// Some tests include promise resolutions which may mean the test code takes a couple of event loop visits itself. So go
+// around an extra 2 times to avoid complicating those tests.
+self.flushAsyncEvents = () => delay(0).then(() => delay(0)).then(() => delay(0)).then(() => delay(0));
+
+self.assert_typed_array_equals = (actual, expected, message) => {
+  const prefix = message === undefined ? '' : `${message} `;
+  assert_equals(typeof actual, 'object', `${prefix}type is object`);
+  assert_equals(actual.constructor, expected.constructor, `${prefix}constructor`);
+  assert_equals(actual.byteOffset, expected.byteOffset, `${prefix}byteOffset`);
+  assert_equals(actual.byteLength, expected.byteLength, `${prefix}byteLength`);
+  assert_equals(actual.buffer.byteLength, expected.buffer.byteLength, `${prefix}buffer.byteLength`);
+  assert_array_equals([...actual], [...expected], `${prefix}contents`);
+  assert_array_equals([...new Uint8Array(actual.buffer)], [...new Uint8Array(expected.buffer)], `${prefix}buffer contents`);
+};
+
+self.makePromiseAndResolveFunc = () => {
+  let resolve;
+  const promise = new Promise(r => { resolve = r; });
+  return [promise, resolve];
+};
diff --git a/testing/web-platform/tests/streams/transferable/deserialize-error.window.js b/testing/web-platform/tests/streams/transferable/deserialize-error.window.js
new file mode 100644
index 0000000000..64cf2bbfb1
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/deserialize-error.window.js
@@ -0,0 +1,39 @@
+// META: script=/common/get-host-info.sub.js
+// META: script=resources/create-wasm-module.js
+// META: timeout=long
+
+const { HTTPS_NOTSAMESITE_ORIGIN } = get_host_info();
+const iframe = document.createElement('iframe');
+iframe.src = `${HTTPS_NOTSAMESITE_ORIGIN}/streams/transferable/resources/deserialize-error-frame.html`;
+
+window.addEventListener('message', async evt => {
+  // Tests are serialized to make the results deterministic.
+  switch (evt.data) {
+    case 'init done': {
+      const ws = new WritableStream();
+      iframe.contentWindow.postMessage(ws, '*', [ws]);
+      return;
+    }
+
+    case 'ws done': {
+      const module = await createWasmModule();
+      const rs = new ReadableStream({
+        start(controller) {
+          controller.enqueue(module);
+        }
+      });
+      iframe.contentWindow.postMessage(rs, '*', [rs]);
+      return;
+    }
+
+    case 'rs done': {
+      iframe.remove();
+    }
+  }
+});
+
+// Need to do this after adding the listener to ensure we catch the first
+// message.
+document.body.appendChild(iframe);
+
+fetch_tests_from_window(iframe.contentWindow);
diff --git a/testing/web-platform/tests/streams/transferable/gc-crash.html b/testing/web-platform/tests/streams/transferable/gc-crash.html
new file mode 100644
index 0000000000..0d331e6be0
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/gc-crash.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html class="test-wait">
+<script src="/common/gc.js"></script>
+<script type="module">
+  const b = new ReadableStream({
+    start(c) {
+      c.enqueue({}) // the value we will transfer
+    },
+  })
+  const transferred = structuredClone(b, { transfer: [b] })
+  // Here we request a read, triggering a message transfer
+  transferred.getReader().read()
+  // And immediately trigger GC without waiting for the read,
+  // causing the actual transfer to be done after GC
+  await garbageCollect()
+  document.documentElement.classList.remove("test-wait")
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/readable-stream.html b/testing/web-platform/tests/streams/transferable/readable-stream.html
new file mode 100644
index 0000000000..b1ede4695b
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/readable-stream.html
@@ -0,0 +1,260 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/helpers.js"></script>
+<script src="../resources/recording-streams.js"></script>
+<script src="../resources/test-utils.js"></script>
+<script>
+'use strict';
+
+promise_test(async () => {
+  const rs = await createTransferredReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.close();
+    }
+  });
+  const reader = rs.getReader();
+  {
+    const {value, done} = await reader.read();
+    assert_false(done, 'should not be done yet');
+    assert_equals(value, 'a', 'first chunk should be a');
+  }
+  {
+    const {done} = await reader.read();
+    assert_true(done, 'should be done now');
+  }
+}, 'sending one chunk through a transferred stream should work');
+
+promise_test(async () => {
+  let controller;
+  const rs = await createTransferredReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  for (let i = 0; i < 10; ++i) {
+    controller.enqueue(i);
+  }
+  controller.close();
+  const reader = rs.getReader();
+  for (let i = 0; i < 10; ++i) {
+    const {value, done} = await reader.read();
+    assert_false(done, 'should not be done yet');
+    assert_equals(value, i, 'chunk content should match index');
+  }
+  const {done} = await reader.read();
+  assert_true(done, 'should be done now');
+}, 'sending ten chunks through a transferred stream should work');
+
+promise_test(async () => {
+  let controller;
+  const rs = await createTransferredReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const reader = rs.getReader();
+  for (let i = 0; i < 10; ++i) {
+    controller.enqueue(i);
+    const {value, done} = await reader.read();
+    assert_false(done, 'should not be done yet');
+    assert_equals(value, i, 'chunk content should match index');
+  }
+  controller.close();
+  const {done} = await reader.read();
+  assert_true(done, 'should be done now');
+}, 'sending ten chunks one at a time should work');
+
+promise_test(async () => {
+  let controller;
+  const rs = await createTransferredReadableStream({
+    start() {
+      this.counter = 0;
+    },
+    pull(controller) {
+      controller.enqueue(this.counter);
+      ++this.counter;
+      if (this.counter === 10)
+        controller.close();
+    }
+  });
+  const reader = rs.getReader();
+  for (let i = 0; i < 10; ++i) {
+    const {value, done} = await reader.read();
+    assert_false(done, 'should not be done yet');
+    assert_equals(value, i, 'chunk content should match index');
+  }
+  const {done} = await reader.read();
+  assert_true(done, 'should be done now');
+}, 'sending ten chunks on demand should work');
+
+promise_test(async () => {
+  const rs = recordingReadableStream({}, { highWaterMark: 0 });
+  await delay(0);
+  assert_array_equals(rs.events, [], 'pull() should not have been called');
+  // Eat the message so it can't interfere with other tests.
+  addEventListener('message', () => {}, {once: true});
+  // The transfer is done manually to verify that it is posting the stream that
+  // relieves backpressure, not receiving it.
+  postMessage(rs, '*', [rs]);
+  await delay(0);
+  assert_array_equals(rs.events, ['pull'], 'pull() should have been called');
+}, 'transferring a stream should relieve backpressure');
+
+promise_test(async () => {
+  const rs = await recordingTransferredReadableStream({
+    pull(controller) {
+      controller.enqueue('a');
+    }
+  }, { highWaterMark: 2 });
+  await delay(0);
+  assert_array_equals(rs.events, ['pull', 'pull', 'pull'],
+                      'pull() should have been called three times');
+}, 'transferring a stream should add one chunk to the queue size');
+
+promise_test(async () => {
+  const rs = await recordingTransferredReadableStream({
+    start(controller) {
+      controller.enqueue(new Uint8Array(1024));
+      controller.enqueue(new Uint8Array(1024));
+    }
+  }, new ByteLengthQueuingStrategy({highWaterMark: 512}));
+  await delay(0);
+  // At this point the queue contains 1024/512 bytes and 1/1 chunk, so it's full
+  // and pull() is not called.
+  assert_array_equals(rs.events, [], 'pull() should not have been called');
+  const reader = rs.getReader();
+  const {value, done} = await reader.read();
+  assert_false(done, 'we should not be done');
+  assert_equals(value.byteLength, 1024, 'expected chunk should be returned');
+  // Now the queue contains 0/512 bytes and 1/1 chunk, so pull() is called. If
+  // the implementation erroneously counted the extra queue space in bytes, then
+  // the queue would contain 1024/513 bytes and pull() wouldn't be called.
+  assert_array_equals(rs.events, ['pull'], 'pull() should have been called');
+}, 'the extra queue from transferring is counted in chunks');
+
+async function transferredReadableStreamWithCancelPromise() {
+  let resolveCancelCalled;
+  const cancelCalled = new Promise(resolve => {
+    resolveCancelCalled = resolve;
+  });
+  const rs = await recordingTransferredReadableStream({
+    cancel() {
+      resolveCancelCalled();
+    }
+  });
+  return { rs, cancelCalled };
+}
+
+promise_test(async () => {
+  const { rs, cancelCalled } = await transferredReadableStreamWithCancelPromise();
+  rs.cancel('message');
+  await cancelCalled;
+  assert_array_equals(rs.events, ['pull', 'cancel', 'message'],
+                      'cancel() should have been called');
+  const reader = rs.getReader();
+  // Check the stream really got closed.
+  await reader.closed;
+}, 'cancel should be propagated to the original');
+
+promise_test(async () => {
+  const { rs, cancelCalled } = await transferredReadableStreamWithCancelPromise();
+  const reader = rs.getReader();
+  const readPromise = reader.read();
+  reader.cancel('done');
+  const { done } = await readPromise;
+  assert_true(done, 'should be done');
+  await cancelCalled;
+  assert_array_equals(rs.events, ['pull', 'cancel', 'done'],
+                      'events should match');
+}, 'cancel should abort a pending read()');
+
+promise_test(async () => {
+  let cancelComplete = false;
+  const rs = await createTransferredReadableStream({
+    async cancel() {
+      await flushAsyncEvents();
+      cancelComplete = true;
+    }
+  });
+  await rs.cancel();
+  assert_false(cancelComplete,
+               'cancel() on the underlying sink should not have completed');
+}, 'stream cancel should not wait for underlying source cancel');
+
+promise_test(async t => {
+  const rs = await recordingTransferredReadableStream();
+  const reader = rs.getReader();
+  let serializationHappened = false;
+  rs.controller.enqueue({
+    get getter() {
+      serializationHappened = true;
+      return 'a';
+    }
+  });
+  await flushAsyncEvents();
+  assert_false(serializationHappened,
+               'serialization should not have happened yet');
+  const {value, done} = await reader.read();
+  assert_false(done, 'should not be done');
+  assert_equals(value.getter, 'a', 'getter should be a');
+  assert_true(serializationHappened,
+              'serialization should have happened');
+}, 'serialization should not happen until the value is read');
+
+promise_test(async t => {
+  const rs = await recordingTransferredReadableStream();
+  const reader = rs.getReader();
+  rs.controller.enqueue(new ReadableStream());
+  await promise_rejects_dom(t, 'DataCloneError', reader.read(),
+                            'closed promise should reject');
+  assert_throws_js(TypeError, () => rs.controller.enqueue(),
+                   'original stream should be errored');
+}, 'transferring a non-serializable chunk should error both sides');
+
+promise_test(async t => {
+  const rs = await createTransferredReadableStream({
+    start(controller) {
+      controller.error('foo');
+    }
+  });
+  const reader = rs.getReader();
+  return promise_rejects_exactly(t, 'foo', reader.read(),
+                                 'error should be passed through');
+}, 'errors should be passed through');
+
+promise_test(async () => {
+  const rs = await recordingTransferredReadableStream();
+  await delay(0);
+  const reader = rs.getReader();
+  reader.cancel();
+  rs.controller.error();
+  const {done} = await reader.read();
+  assert_true(done, 'should be done');
+  assert_throws_js(TypeError, () => rs.controller.enqueue(),
+                   'enqueue should throw');
+}, 'race between cancel() and error() should leave sides in different states');
+
+promise_test(async () => {
+  const rs = await recordingTransferredReadableStream();
+  await delay(0);
+  const reader = rs.getReader();
+  reader.cancel();
+  rs.controller.close();
+  const {done} = await reader.read();
+  assert_true(done, 'should be done');
+}, 'race between cancel() and close() should be benign');
+
+promise_test(async () => {
+  const rs = await recordingTransferredReadableStream();
+  await delay(0);
+  const reader = rs.getReader();
+  reader.cancel();
+  rs.controller.enqueue('a');
+  const {done} = await reader.read();
+  assert_true(done, 'should be done');
+}, 'race between cancel() and enqueue() should be benign');
+
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/reason.html b/testing/web-platform/tests/streams/transferable/reason.html
new file mode 100644
index 0000000000..4251aa85b8
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/reason.html
@@ -0,0 +1,132 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/helpers.js"></script>
+<script>
+'use strict';
+
+// Chrome used to special-case the reason for cancel() and abort() in order to
+// handle exceptions correctly. This is no longer necessary. These tests are
+// retained to avoid regressions.
+
+async function getTransferredReason(originalReason) {
+  let resolvePromise;
+  const rv = new Promise(resolve => {
+    resolvePromise = resolve;
+  });
+  const rs = await createTransferredReadableStream({
+    cancel(reason) {
+      resolvePromise(reason);
+    }
+  });
+  await rs.cancel(originalReason);
+  return rv;
+}
+
+for (const value of ['hi', '\t\r\n', 7, 3.0, undefined, null, true, false,
+                    NaN, Infinity]) {
+  promise_test(async () => {
+    const reason = await getTransferredReason(value);
+    assert_equals(reason, value, 'reason should match');
+  }, `reason with a simple value of '${value}' should be preserved`);
+}
+
+for (const badType of [Symbol('hi'), _ => 'hi']) {
+  promise_test(async t => {
+    return promise_rejects_dom(t, 'DataCloneError',
+                               getTransferredReason(badType),
+                               'cancel() should reject');
+  }, `reason with a type of '${typeof badType}' should be rejected and ` +
+     `error the stream`);
+}
+
+promise_test(async () => {
+  const reasonAsJson =
+        `{"foo":[1,"col"],"bar":{"hoge":0.2,"baz":{},"shan":null}}`;
+  const reason = await getTransferredReason(JSON.parse(reasonAsJson));
+  assert_equals(JSON.stringify(reason), reasonAsJson,
+                'object should be preserved');
+}, 'objects that can be completely expressed in JSON should be preserved');
+
+promise_test(async () => {
+  const circularObject = {};
+  circularObject.self = circularObject;
+  const reason = await getTransferredReason(circularObject);
+  assert_true(reason instanceof Object, 'an Object should be output');
+  assert_equals(reason.self, reason,
+                'the object should have a circular reference');
+}, 'objects that cannot be expressed in JSON should also be preserved');
+
+promise_test(async () => {
+  const originalReason = new TypeError('hi');
+  const reason = await getTransferredReason(originalReason);
+  assert_true(reason instanceof TypeError,
+              'type should be preserved');
+  assert_equals(reason.message, originalReason.message,
+                'message should be preserved');
+}, 'the type and message of a TypeError should be preserved');
+
+promise_test(async () => {
+  const originalReason = new TypeError('hi');
+  originalReason.foo = 'bar';
+  const reason = await getTransferredReason(originalReason);
+  assert_false('foo' in reason,
+               'foo should not be preserved');
+}, 'other attributes of a TypeError should not be preserved');
+
+promise_test(async () => {
+  const originalReason = new TypeError();
+  originalReason.message = [1, 2, 3];
+  const reason = await getTransferredReason(originalReason);
+  assert_equals(reason.message, '1,2,3', 'message should be stringified');
+}, 'a TypeError message should be converted to a string');
+
+promise_test(async () => {
+  const originalReason = new TypeError();
+  Object.defineProperty(originalReason, 'message', {
+    get() { return 'words'; }
+  });
+  const reason = await getTransferredReason(originalReason);
+  assert_equals(reason.message, '', 'message should not be preserved');
+}, 'a TypeError message should not be preserved if it is a getter');
+
+promise_test(async () => {
+  const originalReason = new TypeError();
+  delete originalReason.message;
+  TypeError.prototype.message = 'inherited message';
+  const reason = await getTransferredReason(originalReason);
+  delete TypeError.prototype.message;
+  assert_equals(reason.message, '', 'message should not be preserved');
+}, 'a TypeError message should not be preserved if it is inherited');
+
+promise_test(async () => {
+  const originalReason = new DOMException('yes', 'AbortError');
+  const reason = await getTransferredReason(originalReason);
+  assert_true(reason instanceof DOMException,
+              'reason should be a DOMException');
+  assert_equals(reason.message, originalReason.message,
+                'the messages should match');
+  assert_equals(reason.name, originalReason.name,
+                'the names should match');
+}, 'DOMException errors should be preserved');
+
+for (const errorConstructor of [EvalError, RangeError,
+                                ReferenceError, SyntaxError, TypeError,
+                                URIError]) {
+  promise_test(async () => {
+    const originalReason = new errorConstructor('nope');
+    const reason = await getTransferredReason(originalReason);
+    assert_equals(typeof reason, 'object', 'reason should have type object');
+    assert_true(reason instanceof errorConstructor,
+                `reason should inherit ${errorConstructor.name}`);
+    assert_true(reason instanceof Error, 'reason should inherit Error');
+    assert_equals(reason.constructor, errorConstructor,
+                  'reason should have the right constructor');
+    assert_equals(reason.name, errorConstructor.name,
+                  `name should match constructor name`);
+    assert_equals(reason.message, 'nope', 'message should match');
+  }, `${errorConstructor.name} should be preserved`);
+}
+
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/resources/create-wasm-module.js b/testing/web-platform/tests/streams/transferable/resources/create-wasm-module.js
new file mode 100644
index 0000000000..37064af95c
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/create-wasm-module.js
@@ -0,0 +1,11 @@
+// There aren't many cloneable types that will cause an error on
+// deserialization. WASM modules have the property that it's an error to
+// deserialize them cross-site, which works for our purposes.
+async function createWasmModule() {
+  // It doesn't matter what the module is, so we use one from another
+  // test.
+  const response =
+        await fetch("/wasm/serialization/module/resources/incrementer.wasm");
+  const ab = await response.arrayBuffer();
+  return WebAssembly.compile(ab);
+}
diff --git a/testing/web-platform/tests/streams/transferable/resources/deserialize-error-frame.html b/testing/web-platform/tests/streams/transferable/resources/deserialize-error-frame.html
new file mode 100644
index 0000000000..5ec2fcda2c
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/deserialize-error-frame.html
@@ -0,0 +1,39 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="create-wasm-module.js"></script>
+<script>
+async_test(t => {
+  parent.postMessage('init done', '*');
+  window.addEventListener('message', async evt => {
+    if (evt.data.constructor.name !== 'WritableStream') {
+      return;
+    }
+    const ws = evt.data;
+    const writer = ws.getWriter();
+    const module = await createWasmModule();
+    writer.write(module);
+    await promise_rejects_dom(t, 'DataCloneError', writer.closed,
+                              'should reject with a DataCloneError');
+    t.done();
+    // Signal that this test is done. When both tests are done the iframe will
+    // be removed.
+    parent.postMessage('ws done', '*');
+  });
+}, 'a WritableStream deserialization failure should result in a DataCloneError');
+
+async_test(t => {
+  window.addEventListener('message', async evt => {
+    if (evt.data.constructor.name !== 'ReadableStream') {
+      return;
+    }
+    const rs = evt.data;
+    const reader = rs.getReader();
+    await promise_rejects_dom(t, 'DataCloneError', reader.read(),
+                              'should reject with a DataCloneError');
+    t.done();
+    // Signal that this test is done. When both tests are done the iframe will
+    // be removed.
+    parent.postMessage('rs done', '*');
+  });
+}, 'a ReadableStream deserialization failure should result in a DataCloneError');
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/resources/echo-iframe.html b/testing/web-platform/tests/streams/transferable/resources/echo-iframe.html
new file mode 100644
index 0000000000..68f6850343
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/echo-iframe.html
@@ -0,0 +1,7 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script>
+addEventListener('message', evt => {
+  evt.source.postMessage(evt.data, '*', [evt.data]);
+});
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/resources/echo-worker.js b/testing/web-platform/tests/streams/transferable/resources/echo-worker.js
new file mode 100644
index 0000000000..806c237108
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/echo-worker.js
@@ -0,0 +1,2 @@
+// A worker that just transfers back any message that is sent to it.
+onmessage = evt => postMessage(evt.data, [evt.data]);
diff --git a/testing/web-platform/tests/streams/transferable/resources/helpers.js b/testing/web-platform/tests/streams/transferable/resources/helpers.js
new file mode 100644
index 0000000000..12504537f9
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/helpers.js
@@ -0,0 +1,132 @@
+'use strict';
+
+(() => {
+  // Create a ReadableStream that will pass the tests in
+  // testTransferredReadableStream(), below.
+  function createOriginalReadableStream() {
+    return new ReadableStream({
+      start(controller) {
+        controller.enqueue('a');
+        controller.close();
+      }
+    });
+  }
+
+  // Common tests to roughly determine that |rs| is a correctly transferred
+  // version of a stream created by createOriginalReadableStream().
+  function testTransferredReadableStream(rs) {
+    assert_equals(rs.constructor, ReadableStream,
+                  'rs should be a ReadableStream in this realm');
+    assert_true(rs instanceof ReadableStream,
+                'instanceof check should pass');
+
+    // Perform a brand-check on |rs| in the process of calling getReader().
+    const reader = ReadableStream.prototype.getReader.call(rs);
+
+    return reader.read().then(({value, done}) => {
+      assert_false(done, 'done should be false');
+      assert_equals(value, 'a', 'value should be "a"');
+      return reader.read();
+    }).then(({done}) => {
+      assert_true(done, 'done should be true');
+    });
+  }
+
+  function testMessage(msg) {
+    assert_array_equals(msg.ports, [], 'there should be no ports in the event');
+    return testTransferredReadableStream(msg.data);
+  }
+
+  function testMessageEvent(target) {
+    return new Promise((resolve, reject) => {
+      target.addEventListener('message', ev => {
+        try {
+          resolve(testMessage(ev));
+        } catch (e) {
+          reject(e);
+        }
+      }, {once: true});
+    });
+  }
+
+  function testMessageEventOrErrorMessage(target) {
+    return new Promise((resolve, reject) => {
+      target.addEventListener('message', ev => {
+        if (typeof ev.data === 'string') {
+          // Assume it's an error message and reject with it.
+          reject(ev.data);
+          return;
+        }
+
+        try {
+          resolve(testMessage(ev));
+        } catch (e) {
+          reject(e);
+        }
+      }, {once: true});
+    });
+  }
+
+  function checkTestResults(target) {
+    return new Promise((resolve, reject) => {
+      target.onmessage = msg => {
+        // testharness.js sends us objects which we need to ignore.
+        if (typeof msg.data !== 'string')
+        return;
+
+        if (msg.data === 'OK') {
+          resolve();
+        } else {
+          reject(msg.data);
+        }
+      };
+    });
+  }
+
+  // These tests assume that a transferred ReadableStream will behave the same
+  // regardless of how it was transferred. This enables us to simply transfer the
+  // stream to ourselves.
+  function createTransferredReadableStream(underlyingSource) {
+    const original = new ReadableStream(underlyingSource);
+    const promise = new Promise((resolve, reject) => {
+      addEventListener('message', msg => {
+        const rs = msg.data;
+        if (rs instanceof ReadableStream) {
+          resolve(rs);
+        } else {
+          reject(new Error(`what is this thing: "${rs}"?`));
+        }
+      }, {once: true});
+    });
+    postMessage(original, '*', [original]);
+    return promise;
+  }
+
+  function recordingTransferredReadableStream(underlyingSource, strategy) {
+    const original = recordingReadableStream(underlyingSource, strategy);
+    const promise = new Promise((resolve, reject) => {
+      addEventListener('message', msg => {
+        const rs = msg.data;
+        if (rs instanceof ReadableStream) {
+          rs.events = original.events;
+          rs.eventsWithoutPulls = original.eventsWithoutPulls;
+          rs.controller = original.controller;
+          resolve(rs);
+        } else {
+          reject(new Error(`what is this thing: "${rs}"?`));
+        }
+      }, {once: true});
+    });
+    postMessage(original, '*', [original]);
+    return promise;
+  }
+
+  self.createOriginalReadableStream = createOriginalReadableStream;
+  self.testMessage = testMessage;
+  self.testMessageEvent = testMessageEvent;
+  self.testMessageEventOrErrorMessage = testMessageEventOrErrorMessage;
+  self.checkTestResults = checkTestResults;
+  self.createTransferredReadableStream = createTransferredReadableStream;
+  self.recordingTransferredReadableStream = recordingTransferredReadableStream;
+
+})();
diff --git a/testing/web-platform/tests/streams/transferable/resources/receiving-shared-worker.js b/testing/web-platform/tests/streams/transferable/resources/receiving-shared-worker.js
new file mode 100644
index 0000000000..84f779c3db
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/receiving-shared-worker.js
@@ -0,0 +1,11 @@
+'use strict';
+importScripts('/resources/testharness.js', 'helpers.js');
+
+onconnect = evt => {
+  const port = evt.source;
+  const promise = testMessageEvent(port);
+  port.start();
+  promise
+      .then(() => port.postMessage('OK'))
+      .catch(err => port.postMessage(`BAD: ${err}`));
+};
diff --git a/testing/web-platform/tests/streams/transferable/resources/receiving-worker.js b/testing/web-platform/tests/streams/transferable/resources/receiving-worker.js
new file mode 100644
index 0000000000..4ebb9c5f8f
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/receiving-worker.js
@@ -0,0 +1,7 @@
+'use strict';
+importScripts('/resources/testharness.js', 'helpers.js');
+
+const promise = testMessageEvent(self);
+promise
+    .then(() => postMessage('OK'))
+    .catch(err => postMessage(`BAD: ${err}`));
diff --git a/testing/web-platform/tests/streams/transferable/resources/sending-shared-worker.js b/testing/web-platform/tests/streams/transferable/resources/sending-shared-worker.js
new file mode 100644
index 0000000000..e579077894
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/sending-shared-worker.js
@@ -0,0 +1,12 @@
+'use strict';
+importScripts('helpers.js');
+
+onconnect = msg => {
+  const port = msg.source;
+  const orig = createOriginalReadableStream();
+  try {
+    port.postMessage(orig, [orig]);
+  } catch (e) {
+    port.postMessage(e.message);
+  }
+};
diff --git a/testing/web-platform/tests/streams/transferable/resources/sending-worker.js b/testing/web-platform/tests/streams/transferable/resources/sending-worker.js
new file mode 100644
index 0000000000..0b79733f74
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/sending-worker.js
@@ -0,0 +1,5 @@
+'use strict';
+importScripts('helpers.js');
+
+const orig = createOriginalReadableStream();
+postMessage(orig, [orig]);
diff --git a/testing/web-platform/tests/streams/transferable/resources/service-worker-iframe.html b/testing/web-platform/tests/streams/transferable/resources/service-worker-iframe.html
new file mode 100644
index 0000000000..348d067c92
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/service-worker-iframe.html
@@ -0,0 +1,39 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="helpers.js"></script>
+<script>
+'use strict';
+
+setup({
+  explicit_done: true
+});
+
+function startTests() {
+  promise_test(() => {
+    const orig = createOriginalReadableStream();
+    const promise = checkTestResults(navigator.serviceWorker);
+    navigator.serviceWorker.controller.postMessage(orig, [orig]);
+    assert_true(orig.locked, 'the original stream should be locked');
+    return promise;
+  }, 'serviceWorker.controller.postMessage should be able to transfer a ' +
+               'ReadableStream');
+
+  promise_test(() => {
+    const promise = testMessageEventOrErrorMessage(navigator.serviceWorker);
+    navigator.serviceWorker.controller.postMessage('SEND');
+    return promise;
+  }, 'postMessage in a service worker should be able to transfer ReadableStream');
+
+  done();
+}
+
+// Delay running the tests until we get a message from the page telling us to.
+// This is to work around an issue where testharness.js doesn't detect
+// completion of the tests if they fail too early.
+onmessage = msg => {
+  if (msg.data === 'explicit trigger')
+    startTests();
+};
+
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/resources/service-worker.js b/testing/web-platform/tests/streams/transferable/resources/service-worker.js
new file mode 100644
index 0000000000..af76b6c11b
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/resources/service-worker.js
@@ -0,0 +1,30 @@
+'use strict';
+importScripts('/resources/testharness.js', 'helpers.js');
+
+onmessage = msg => {
+  const client = msg.source;
+  if (msg.data === 'SEND') {
+    sendingTest(client);
+  } else {
+    receivingTest(msg, client);
+  }
+};
+
+function sendingTest(client) {
+  const orig = createOriginalReadableStream();
+  try {
+    client.postMessage(orig, [orig]);
+  } catch (e) {
+    client.postMessage(e.message);
+  }
+}
+
+function receivingTest(msg, client) {
+  try {
+    msg.waitUntil(testMessage(msg)
+                  .then(() => client.postMessage('OK'))
+                  .catch(e => client.postMessage(`BAD: ${e}`)));
+  } catch (e) {
+    client.postMessage(`BAD: ${e}`);
+  }
+}
diff --git a/testing/web-platform/tests/streams/transferable/service-worker.https.html b/testing/web-platform/tests/streams/transferable/service-worker.https.html
new file mode 100644
index 0000000000..2ca7f19c91
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/service-worker.https.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/service-workers/service-worker/resources/test-helpers.sub.js"></script>
+<script>
+'use strict';
+
+const kServiceWorkerUrl = 'resources/service-worker.js';
+const kIframeUrl = 'resources/service-worker-iframe.html';
+
+// A dummy test so that we can use the test-helpers.sub.js functions
+const test = async_test('service-worker');
+
+async function registerAndStart() {
+  const reg = await service_worker_unregister_and_register(
+    test, kServiceWorkerUrl, kIframeUrl);
+  await wait_for_state(test, reg.installing, 'activated');
+  const iframe = await with_iframe(kIframeUrl);
+  fetch_tests_from_window(iframe.contentWindow);
+  add_completion_callback(() => iframe.remove());
+  iframe.contentWindow.postMessage('explicit trigger', '*');
+  return service_worker_unregister_and_done(test, kIframeUrl);
+}
+
+onload = registerAndStart;
+
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/shared-worker.html b/testing/web-platform/tests/streams/transferable/shared-worker.html
new file mode 100644
index 0000000000..cd0415402d
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/shared-worker.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/helpers.js"></script>
+<script>
+'use strict';
+
+promise_test(t => {
+  const orig = createOriginalReadableStream();
+  const w = new SharedWorker('resources/receiving-shared-worker.js');
+  const promise = checkTestResults(w.port);
+  w.port.postMessage(orig, [orig]);
+  assert_true(orig.locked, 'the original stream should be locked');
+  return promise;
+}, 'worker.postMessage should be able to transfer a ReadableStream');
+
+promise_test(t => {
+  const w = new SharedWorker('resources/sending-shared-worker.js');
+  const promise = testMessageEventOrErrorMessage(w.port);
+  w.port.start();
+  return promise;
+}, 'postMessage in a worker should be able to transfer a ReadableStream');
+
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/transfer-with-messageport.window.js b/testing/web-platform/tests/streams/transferable/transfer-with-messageport.window.js
new file mode 100644
index 0000000000..37f8c9df16
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/transfer-with-messageport.window.js
@@ -0,0 +1,219 @@
+"use strict";
+
+function receiveEventOnce(target, name) {
+  return new Promise(resolve => {
+    target.addEventListener(
+      name,
+      ev => {
+        resolve(ev);
+      },
+      { once: true }
+    );
+  });
+}
+
+async function postAndTestMessageEvent(data, transfer, title) {
+  postMessage(data, "*", transfer);
+  const messagePortCount = transfer.filter(i => i instanceof MessagePort)
+    .length;
+  const ev = await receiveEventOnce(window, "message");
+  assert_equals(
+    ev.ports.length,
+    messagePortCount,
+    `Correct number of ports ${title}`
+  );
+  for (const [i, port] of ev.ports.entries()) {
+    assert_true(
+      port instanceof MessagePort,
+      `ports[${i}] include MessagePort ${title}`
+    );
+  }
+  for (const [key, value] of Object.entries(data)) {
+    assert_true(
+      ev.data[key] instanceof value.constructor,
+      `data.${key} has correct interface ${value.constructor.name} ${title}`
+    );
+  }
+}
+
+async function transferMessagePortWithOrder1(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    { stream, port2: channel.port2 },
+    [stream, channel.port2],
+    `when transferring [${stream.constructor.name}, MessagePort]`
+  );
+}
+
+async function transferMessagePortWithOrder2(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    { stream, port2: channel.port2 },
+    [channel.port2, stream],
+    `when transferring [MessagePort, ${stream.constructor.name}]`
+  );
+}
+
+async function transferMessagePortWithOrder3(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    { port1: channel.port1, stream, port2: channel.port2 },
+    [channel.port1, stream, channel.port2],
+    `when transferring [MessagePort, ${stream.constructor.name}, MessagePort]`
+  );
+}
+
+async function transferMessagePortWithOrder4(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    {},
+    [channel.port1, stream, channel.port2],
+    `when transferring [MessagePort, ${stream.constructor.name}, MessagePort] but with empty data`
+  );
+}
+
+async function transferMessagePortWithOrder5(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    { port2: channel.port2, port1: channel.port1, stream },
+    [channel.port1, stream, channel.port2],
+    `when transferring [MessagePort, ${stream.constructor.name}, MessagePort] but with data having different order`
+  );
+}
+
+async function transferMessagePortWithOrder6(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    { port2: channel.port2, port1: channel.port1 },
+    [channel.port1, stream, channel.port2],
+    `when transferring [MessagePort, ${stream.constructor.name}, MessagePort] but with stream not being in the data`
+  );
+}
+
+async function transferMessagePortWithOrder7(stream) {
+  const channel = new MessageChannel();
+  await postAndTestMessageEvent(
+    { stream },
+    [channel.port1, stream, channel.port2],
+    `when transferring [MessagePort, ${stream.constructor.name}, MessagePort] but with ports not being in the data`
+  );
+}
+
+async function transferMessagePortWith(constructor) {
+  await transferMessagePortWithOrder1(new constructor());
+  await transferMessagePortWithOrder2(new constructor());
+  await transferMessagePortWithOrder3(new constructor());
+}
+
+async function advancedTransferMesagePortWith(constructor) {
+  await transferMessagePortWithOrder4(new constructor());
+  await transferMessagePortWithOrder5(new constructor());
+  await transferMessagePortWithOrder6(new constructor());
+  await transferMessagePortWithOrder7(new constructor());
+}
+
+async function mixedTransferMessagePortWithOrder1() {
+  const channel = new MessageChannel();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  const transform = new TransformStream();
+  await postAndTestMessageEvent(
+    {
+      readable,
+      writable,
+      transform,
+      port1: channel.port1,
+      port2: channel.port2,
+    },
+    [readable, writable, transform, channel.port1, channel.port2],
+    `when transferring [ReadableStream, WritableStream, TransformStream, MessagePort, MessagePort]`
+  );
+}
+
+async function mixedTransferMessagePortWithOrder2() {
+  const channel = new MessageChannel();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  const transform = new TransformStream();
+  await postAndTestMessageEvent(
+    { readable, writable, transform },
+    [transform, channel.port1, readable, channel.port2, writable],
+    `when transferring [TransformStream, MessagePort, ReadableStream, MessagePort, WritableStream]`
+  );
+}
+
+async function mixedTransferMessagePortWithOrder3() {
+  const channel = new MessageChannel();
+  const readable1 = new ReadableStream();
+  const readable2 = new ReadableStream();
+  const writable1 = new WritableStream();
+  const writable2 = new WritableStream();
+  const transform1 = new TransformStream();
+  const transform2 = new TransformStream();
+  await postAndTestMessageEvent(
+    { readable1, writable1, transform1, readable2, writable2, transform2 },
+    [
+      transform2,
+      channel.port1,
+      readable1,
+      channel.port2,
+      writable2,
+      readable2,
+      writable1,
+      transform1,
+    ],
+    `when transferring [TransformStream, MessagePort, ReadableStream, MessagePort, WritableStream, ReadableStream, WritableStream, TransformStream] but with the data having different order`
+  );
+}
+
+async function mixedTransferMesagePortWith() {
+  await mixedTransferMessagePortWithOrder1();
+  await mixedTransferMessagePortWithOrder2();
+  await mixedTransferMessagePortWithOrder3();
+}
+
+promise_test(async t => {
+  await transferMessagePortWith(ReadableStream);
+}, "Transferring a MessagePort with a ReadableStream should set `.ports`");
+
+promise_test(async t => {
+  await transferMessagePortWith(WritableStream);
+}, "Transferring a MessagePort with a WritableStream should set `.ports`");
+
+promise_test(async t => {
+  await transferMessagePortWith(TransformStream);
+}, "Transferring a MessagePort with a TransformStream should set `.ports`");
+
+promise_test(async t => {
+  await transferMessagePortWith(ReadableStream);
+}, "Transferring a MessagePort with a ReadableStream should set `.ports`, advanced");
+
+promise_test(async t => {
+  await transferMessagePortWith(WritableStream);
+}, "Transferring a MessagePort with a WritableStream should set `.ports`, advanced");
+
+promise_test(async t => {
+  await transferMessagePortWith(TransformStream);
+}, "Transferring a MessagePort with a TransformStream should set `.ports`, advanced");
+
+promise_test(async t => {
+  await mixedTransferMesagePortWith();
+}, "Transferring a MessagePort with multiple streams should set `.ports`");
+
+test(() => {
+  assert_throws_dom("DataCloneError", () =>
+    postMessage({ stream: new ReadableStream() }, "*")
+  );
+}, "ReadableStream must not be serializable");
+
+test(() => {
+  assert_throws_dom("DataCloneError", () =>
+    postMessage({ stream: new WritableStream() }, "*")
+  );
+}, "WritableStream must not be serializable");
+
+test(() => {
+  assert_throws_dom("DataCloneError", () =>
+    postMessage({ stream: new TransformStream() }, "*")
+  );
+}, "TransformStream must not be serializable");
diff --git a/testing/web-platform/tests/streams/transferable/transform-stream-members.any.js b/testing/web-platform/tests/streams/transferable/transform-stream-members.any.js
new file mode 100644
index 0000000000..fca060b0c0
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/transform-stream-members.any.js
@@ -0,0 +1,16 @@
+const combinations = [
+  (t => [t, t.readable])(new TransformStream()),
+  (t => [t.readable, t])(new TransformStream()),
+  (t => [t, t.writable])(new TransformStream()),
+  (t => [t.writable, t])(new TransformStream()),
+];
+
+for (const combination of combinations) {
+  test(() => {
+    assert_throws_dom(
+      "DataCloneError",
+      () => structuredClone(combination, { transfer: combination }),
+      "structuredClone should throw"
+    );
+  }, `Transferring ${combination} should fail`);
+}
diff --git a/testing/web-platform/tests/streams/transferable/transform-stream.html b/testing/web-platform/tests/streams/transferable/transform-stream.html
new file mode 100644
index 0000000000..355d5d8074
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/transform-stream.html
@@ -0,0 +1,108 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../resources/test-utils.js"></script>
+<script>
+'use strict';
+
+promise_test(t => {
+  const orig = new TransformStream();
+  const promise = new Promise(resolve => {
+    addEventListener('message', t.step_func(evt => {
+      const transferred = evt.data;
+      assert_equals(transferred.constructor, TransformStream,
+                    'transferred should be a TransformStream in this realm');
+      assert_true(transferred instanceof TransformStream,
+                  'instanceof check should pass');
+
+      // Perform a brand-check on |transferred|.
+      const readableGetter = Object.getOwnPropertyDescriptor(
+        TransformStream.prototype, 'readable').get;
+      assert_true(readableGetter.call(transferred) instanceof ReadableStream,
+                 'brand check should pass and readable stream should result');
+      const writableGetter = Object.getOwnPropertyDescriptor(
+        TransformStream.prototype, 'writable').get;
+      assert_true(writableGetter.call(transferred) instanceof WritableStream,
+                 'brand check should pass and writable stream should result');
+      resolve();
+    }), {once: true});
+  });
+  postMessage(orig, '*', [orig]);
+  assert_true(orig.readable.locked, 'the readable side should be locked');
+  assert_true(orig.writable.locked, 'the writable side should be locked');
+  return promise;
+}, 'window.postMessage should be able to transfer a TransformStream');
+
+test(() => {
+  const ts = new TransformStream();
+  const writer = ts.writable.getWriter();
+  assert_throws_dom('DataCloneError', () => postMessage(ts, '*', [ts]),
+                    'postMessage should throw');
+  assert_false(ts.readable.locked, 'readable side should not get locked');
+}, 'a TransformStream with a locked writable should not be transferable');
+
+test(() => {
+  const ts = new TransformStream();
+  const reader = ts.readable.getReader();
+  assert_throws_dom('DataCloneError', () => postMessage(ts, '*', [ts]),
+                    'postMessage should throw');
+  assert_false(ts.writable.locked, 'writable side should not get locked');
+}, 'a TransformStream with a locked readable should not be transferable');
+
+test(() => {
+  const ts = new TransformStream();
+  const reader = ts.readable.getReader();
+  const writer = ts.writable.getWriter();
+  assert_throws_dom('DataCloneError', () => postMessage(ts, '*', [ts]),
+                    'postMessage should throw');
+}, 'a TransformStream with both sides locked should not be transferable');
+
+promise_test(t => {
+  const source = new ReadableStream({
+    start(controller) {
+      controller.enqueue('hello ');
+      controller.enqueue('there ');
+      controller.close();
+    }
+  });
+  let resolve;
+  const ready = new Promise(r => resolve = r);
+  let result = '';
+  const sink = new WritableStream({
+    write(chunk) {
+      if (result) {
+        resolve();
+      }
+      result += chunk;
+    }
+  });
+  const transform1 = new TransformStream({
+    transform(chunk, controller) {
+      controller.enqueue(chunk.toUpperCase());
+    }
+  });
+  const transform2 = new TransformStream({
+    transform(chunk, controller) {
+      controller.enqueue(chunk + chunk);
+    }
+  });
+  const promise = new Promise(resolve => {
+    addEventListener('message', t.step_func(evt => {
+      const data = evt.data;
+      resolve(data.source
+                .pipeThrough(data.transform1)
+                .pipeThrough(data.transform2)
+                .pipeTo(data.sink));
+    }));
+  });
+  postMessage({source, sink, transform1, transform2}, '*',
+              [source, transform1, sink, transform2]);
+  return ready
+    .then(() => {
+      assert_equals(result, 'HELLO HELLO THERE THERE ',
+                    'transforms should have been applied');
+    });
+}, 'piping through transferred transforms should work');
+
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/window.html b/testing/web-platform/tests/streams/transferable/window.html
new file mode 100644
index 0000000000..11c868356b
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/window.html
@@ -0,0 +1,55 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/helpers.js"></script>
+<script>
+'use strict';
+
+promise_test(t => {
+  const orig = createOriginalReadableStream();
+  const promise = testMessageEvent(window);
+  postMessage(orig, '*', [orig]);
+  assert_true(orig.locked, 'the original stream should be locked');
+  return promise;
+}, 'window.postMessage should be able to transfer a ReadableStream');
+
+promise_test(t => {
+  const orig = createOriginalReadableStream();
+  const mc = new MessageChannel();
+  const promise = testMessageEvent(mc.port1);
+  mc.port1.start();
+
+  mc.port2.postMessage(orig, [orig]);
+  mc.port2.close();
+  assert_true(orig.locked, 'the original stream should be locked');
+  return promise;
+}, 'port.postMessage should be able to transfer a ReadableStream');
+
+promise_test(t => {
+  const orig = createOriginalReadableStream();
+  const promise = new Promise(resolve => {
+    addEventListener('message', t.step_func(evt => {
+      const [rs1, rs2] = evt.data;
+      assert_equals(rs1, rs2, 'both ReadableStreams should be the same object');
+      resolve();
+    }), {once: true});
+  });
+  postMessage([orig, orig], '*', [orig]);
+  return promise;
+}, 'the same ReadableStream posted multiple times should arrive together');
+
+const onloadPromise = new Promise(resolve => onload = resolve);
+
+promise_test(() => {
+  const orig = createOriginalReadableStream();
+  const promise = testMessageEvent(window);
+  return onloadPromise.then(() => {
+    const echoIframe = document.querySelector('#echo');
+    echoIframe.contentWindow.postMessage(orig, '*', [orig]);
+    return promise;
+  });
+}, 'transfer to and from an iframe should work');
+</script>
+
+<iframe id=echo src="resources/echo-iframe.html" style="display:none"></iframe>
diff --git a/testing/web-platform/tests/streams/transferable/worker.html b/testing/web-platform/tests/streams/transferable/worker.html
new file mode 100644
index 0000000000..c5dc9fc62f
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/worker.html
@@ -0,0 +1,76 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/helpers.js"></script>
+<script src="../resources/test-utils.js"></script>
+<script>
+'use strict';
+
+promise_test(t => {
+  const orig = createOriginalReadableStream();
+  const w = new Worker('resources/receiving-worker.js');
+  t.add_cleanup(() => {
+    w.terminate();
+  });
+  const promise = new Promise((resolve, reject) => {
+    checkTestResults(w).then(resolve, reject);
+    w.onerror = () => reject('error in worker');
+  });
+  w.postMessage(orig, [orig]);
+  assert_true(orig.locked, 'the original stream should be locked');
+  return promise;
+}, 'worker.postMessage should be able to transfer a ReadableStream');
+
+promise_test(t => {
+  const w = new Worker('resources/sending-worker.js');
+  t.add_cleanup(() => {
+    w.terminate();
+  });
+  return new Promise((resolve, reject) => {
+    testMessageEvent(w).then(resolve, reject);
+    w.onerror = () => reject('error in worker');
+  });
+}, 'postMessage in a worker should be able to transfer a ReadableStream');
+
+promise_test(async t => {
+  const w = new Worker('resources/echo-worker.js');
+  let controller;
+  const orig = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const targetStream = await new Promise((resolve, reject) => {
+    w.onmessage = evt => resolve(evt.data);
+    w.onerror = () => reject('error in worker');
+    w.postMessage(orig, [orig]);
+  });
+  const reader = targetStream.getReader();
+  const reads = [];
+  // Place a lot of chunks "in transit". This should increase the likelihood
+  // that they is a chunk at each relevant step when the worker is terminated.
+  for (let i = 0; i < 50; ++i) {
+    await delay(0);
+    controller.enqueue(i);
+    const expected = i;
+    reads.push(reader.read().then(({value, done}) => {
+      assert_false(done, 'we should not be done');
+      assert_equals(value, expected, 'value should match expectation');
+    }));
+  }
+  w.terminate();
+  for (let i = 50; i < 60; ++i) {
+    controller.enqueue(i);
+    reads.push(
+      reader.read().then(t.unreached_func('read() should not resolve')));
+    await delay(0);
+  }
+  // We don't expect every read() to complete, but we want to give them a chance
+  // to reject if they're going to.
+  return Promise.race([
+    Promise.all(reads),
+    flushAsyncEvents()
+  ]);
+}, 'terminating a worker should not error the stream');
+</script>
diff --git a/testing/web-platform/tests/streams/transferable/writable-stream.html b/testing/web-platform/tests/streams/transferable/writable-stream.html
new file mode 100644
index 0000000000..7e25dad94d
--- /dev/null
+++ b/testing/web-platform/tests/streams/transferable/writable-stream.html
@@ -0,0 +1,146 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/helpers.js"></script>
+<script src="../resources/test-utils.js"></script>
+<script src="../resources/recording-streams.js"></script>
+<script>
+'use strict';
+
+promise_test(t => {
+  const orig = new WritableStream();
+  const promise = new Promise(resolve => {
+    addEventListener('message', t.step_func(evt => {
+      const transferred = evt.data;
+      assert_equals(transferred.constructor, WritableStream,
+                    'transferred should be a WritableStream in this realm');
+      assert_true(transferred instanceof WritableStream,
+                  'instanceof check should pass');
+
+      // Perform a brand-check on |transferred|.
+      const writer = WritableStream.prototype.getWriter.call(transferred);
+      resolve();
+    }), {once: true});
+  });
+  postMessage(orig, '*', [orig]);
+  assert_true(orig.locked, 'the original stream should be locked');
+  return promise;
+}, 'window.postMessage should be able to transfer a WritableStream');
+
+test(() => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  assert_throws_dom('DataCloneError', () => postMessage(ws, '*', [ws]),
+                    'postMessage should throw');
+}, 'a locked WritableStream should not be transferable');
+
+promise_test(t => {
+  const {writable, readable} = new TransformStream();
+  const promise = new Promise(resolve => {
+    addEventListener('message', t.step_func(async evt => {
+      const {writable, readable} = evt.data;
+      const reader = readable.getReader();
+      const writer = writable.getWriter();
+      const writerPromises = Promise.all([
+        writer.write('hi'),
+        writer.close(),
+      ]);
+      const {value, done} = await reader.read();
+      assert_false(done, 'we should not be done');
+      assert_equals(value, 'hi', 'chunk should have been delivered');
+      const readResult = await reader.read();
+      assert_true(readResult.done, 'readable should be closed');
+      await writerPromises;
+      resolve();
+    }), {once: true});
+  });
+  postMessage({writable, readable}, '*', [writable, readable]);
+  return promise;
+}, 'window.postMessage should be able to transfer a {readable, writable} pair');
+
+function transfer(stream) {
+  return new Promise(resolve => {
+    addEventListener('message', evt => resolve(evt.data), { once: true });
+    postMessage(stream, '*', [stream]);
+  });
+}
+
+promise_test(async () => {
+  const orig = new WritableStream(
+    {}, new ByteLengthQueuingStrategy({ highWaterMark: 65536 }));
+  const transferred = await transfer(orig);
+  const writer = transferred.getWriter();
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+}, 'desiredSize for a newly-transferred stream should be 1');
+
+promise_test(async () => {
+  const orig = new WritableStream({
+    write() {
+      return new Promise(() => {});
+    }
+  });
+  const transferred = await transfer(orig);
+  const writer = transferred.getWriter();
+  await writer.write('a');
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+}, 'effective queue size of a transferred writable should be 2');
+
+promise_test(async () => {
+  const [writeCalled, resolveWriteCalled] = makePromiseAndResolveFunc();
+  let resolveWrite;
+  const orig = new WritableStream({
+    write() {
+      resolveWriteCalled();
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+  const transferred = await transfer(orig);
+  const writer = transferred.getWriter();
+  await writer.write('a');
+  let writeDone = false;
+  const writePromise = writer.write('b').then(() => {
+    writeDone = true;
+  });
+  await writeCalled;
+  assert_false(writeDone, 'second write should not have resolved yet');
+  resolveWrite();
+  await writePromise; // (makes sure this resolves)
+}, 'second write should wait for first underlying write to complete');
+
+async function transferredWritableStreamWithAbortPromise() {
+  const [abortCalled, resolveAbortCalled] = makePromiseAndResolveFunc();
+  const orig = recordingWritableStream({
+    abort() {
+      resolveAbortCalled();
+    }
+  });
+  const transferred = await transfer(orig);
+  return { orig, transferred, abortCalled };
+}
+
+promise_test(async t => {
+  const { orig, transferred, abortCalled } = await transferredWritableStreamWithAbortPromise();
+  transferred.abort('p');
+  await abortCalled;
+  assert_array_equals(orig.events, ['abort', 'p'],
+                      'abort() should have been called');
+}, 'abort() should work');
+
+promise_test(async t => {
+  const { orig, transferred, abortCalled } = await transferredWritableStreamWithAbortPromise();
+  const writer = transferred.getWriter();
+  // A WritableStream object cannot be cloned.
+  await promise_rejects_dom(t, 'DataCloneError', writer.write(new WritableStream()),
+                            'the write should reject');
+  await promise_rejects_dom(t, 'DataCloneError', writer.closed,
+                            'the stream should be errored');
+  await abortCalled;
+  assert_equals(orig.events.length, 2, 'abort should have been called');
+  assert_equals(orig.events[0], 'abort', 'first event should be abort');
+  assert_equals(orig.events[1].name, 'DataCloneError',
+                'reason should be a DataCloneError');
+}, 'writing a unclonable object should error the stream');
+</script>
diff --git a/testing/web-platform/tests/streams/transform-streams/backpressure.any.js b/testing/web-platform/tests/streams/transform-streams/backpressure.any.js
new file mode 100644
index 0000000000..6befba41b7
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/backpressure.any.js
@@ -0,0 +1,195 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+const error1 = new Error('error1 message');
+error1.name = 'error1';
+
+promise_test(() => {
+  const ts = recordingTransformStream();
+  const writer = ts.writable.getWriter();
+  // This call never resolves.
+  writer.write('a');
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ts.events, [], 'transform should not be called');
+  });
+}, 'backpressure allows no transforms with a default identity transform and no reader');
+
+promise_test(() => {
+  const ts = recordingTransformStream({}, undefined, { highWaterMark: 1 });
+  const writer = ts.writable.getWriter();
+  // This call to write() resolves asynchronously.
+  writer.write('a');
+  // This call to write() waits for backpressure that is never relieved and never calls transform().
+  writer.write('b');
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ts.events, ['transform', 'a'], 'transform should be called once');
+  });
+}, 'backpressure only allows one transform() with a identity transform with a readable HWM of 1 and no reader');
+
+promise_test(() => {
+  // Without a transform() implementation, recordingTransformStream() never enqueues anything.
+  const ts = recordingTransformStream({
+    transform() {
+      // Discard all chunks. As a result, the readable side is never full enough to exert backpressure and transform()
+      // keeps being called.
+    }
+  }, undefined, { highWaterMark: 1 });
+  const writer = ts.writable.getWriter();
+  const writePromises = [];
+  for (let i = 0; i < 4; ++i) {
+    writePromises.push(writer.write(i));
+  }
+  return Promise.all(writePromises).then(() => {
+    assert_array_equals(ts.events, ['transform', 0, 'transform', 1, 'transform', 2, 'transform', 3],
+                        'all 4 events should be transformed');
+  });
+}, 'transform() should keep being called as long as there is no backpressure');
+
+promise_test(() => {
+  const ts = new TransformStream({}, undefined, { highWaterMark: 1 });
+  const writer = ts.writable.getWriter();
+  const reader = ts.readable.getReader();
+  const events = [];
+  const writerPromises = [
+    writer.write('a').then(() => events.push('a')),
+    writer.write('b').then(() => events.push('b')),
+    writer.close().then(() => events.push('closed'))];
+  return delay(0).then(() => {
+    assert_array_equals(events, ['a'], 'the first write should have resolved');
+    return reader.read();
+  }).then(({ value, done }) => {
+    assert_false(done, 'done should not be true');
+    assert_equals('a', value, 'value should be "a"');
+    return delay(0);
+  }).then(() => {
+    assert_array_equals(events, ['a', 'b', 'closed'], 'both writes and close() should have resolved');
+    return reader.read();
+  }).then(({ value, done }) => {
+    assert_false(done, 'done should still not be true');
+    assert_equals('b', value, 'value should be "b"');
+    return reader.read();
+  }).then(({ done }) => {
+    assert_true(done, 'done should be true');
+    return writerPromises;
+  });
+}, 'writes should resolve as soon as transform completes');
+
+promise_test(() => {
+  const ts = new TransformStream(undefined, undefined, { highWaterMark: 0 });
+  const writer = ts.writable.getWriter();
+  const reader = ts.readable.getReader();
+  const readPromise = reader.read();
+  writer.write('a');
+  return readPromise.then(({ value, done }) => {
+    assert_false(done, 'not done');
+    assert_equals(value, 'a', 'value should be "a"');
+  });
+}, 'calling pull() before the first write() with backpressure should work');
+
+promise_test(() => {
+  let reader;
+  const ts = recordingTransformStream({
+    transform(chunk, controller) {
+      controller.enqueue(chunk);
+      return reader.read();
+    }
+  }, undefined, { highWaterMark: 1 });
+  const writer = ts.writable.getWriter();
+  reader = ts.readable.getReader();
+  return writer.write('a');
+}, 'transform() should be able to read the chunk it just enqueued');
+
+promise_test(() => {
+  let resolveTransform;
+  const transformPromise = new Promise(resolve => {
+    resolveTransform = resolve;
+  });
+  const ts = recordingTransformStream({
+    transform() {
+      return transformPromise;
+    }
+  }, undefined, new CountQueuingStrategy({ highWaterMark: Infinity }));
+  const writer = ts.writable.getWriter();
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+  return delay(0).then(() => {
+    writer.write('a');
+    assert_array_equals(ts.events, ['transform', 'a']);
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0');
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should still be 0');
+    resolveTransform();
+    return delay(0);
+  }).then(() => {
+    assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+  });
+}, 'blocking transform() should cause backpressure');
+
+promise_test(t => {
+  const ts = new TransformStream();
+  ts.readable.cancel(error1);
+  return promise_rejects_exactly(t, error1, ts.writable.getWriter().closed, 'closed should reject');
+}, 'writer.closed should resolve after readable is canceled during start');
+
+promise_test(t => {
+  const ts = new TransformStream({}, undefined, { highWaterMark: 0 });
+  return delay(0).then(() => {
+    ts.readable.cancel(error1);
+    return promise_rejects_exactly(t, error1, ts.writable.getWriter().closed, 'closed should reject');
+  });
+}, 'writer.closed should resolve after readable is canceled with backpressure');
+
+promise_test(t => {
+  const ts = new TransformStream({}, undefined, { highWaterMark: 1 });
+  return delay(0).then(() => {
+    ts.readable.cancel(error1);
+    return promise_rejects_exactly(t, error1, ts.writable.getWriter().closed, 'closed should reject');
+  });
+}, 'writer.closed should resolve after readable is canceled with no backpressure');
+
+promise_test(() => {
+  const ts = new TransformStream({}, undefined, { highWaterMark: 1 });
+  const writer = ts.writable.getWriter();
+  return delay(0).then(() => {
+    const writePromise = writer.write('a');
+    ts.readable.cancel(error1);
+    return writePromise;
+  });
+}, 'cancelling the readable should cause a pending write to resolve');
+
+promise_test(t => {
+  const rs = new ReadableStream();
+  const ts = new TransformStream();
+  const pipePromise = rs.pipeTo(ts.writable);
+  ts.readable.cancel(error1);
+  return promise_rejects_exactly(t, error1, pipePromise, 'promise returned from pipeTo() should be rejected');
+}, 'cancelling the readable side of a TransformStream should abort an empty pipe');
+
+promise_test(t => {
+  const rs = new ReadableStream();
+  const ts = new TransformStream();
+  const pipePromise = rs.pipeTo(ts.writable);
+  return delay(0).then(() => {
+    ts.readable.cancel(error1);
+    return promise_rejects_exactly(t, error1, pipePromise, 'promise returned from pipeTo() should be rejected');
+  });
+}, 'cancelling the readable side of a TransformStream should abort an empty pipe after startup');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    }
+  });
+  const ts = new TransformStream();
+  const pipePromise = rs.pipeTo(ts.writable);
+  // Allow data to flow into the pipe.
+  return delay(0).then(() => {
+    ts.readable.cancel(error1);
+    return promise_rejects_exactly(t, error1, pipePromise, 'promise returned from pipeTo() should be rejected');
+  });
+}, 'cancelling the readable side of a TransformStream should abort a full pipe');
diff --git a/testing/web-platform/tests/streams/transform-streams/errors.any.js b/testing/web-platform/tests/streams/transform-streams/errors.any.js
new file mode 100644
index 0000000000..0cca4c7547
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/errors.any.js
@@ -0,0 +1,341 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+'use strict';
+
+const thrownError = new Error('bad things are happening!');
+thrownError.name = 'error1';
+
+promise_test(t => {
+  const ts = new TransformStream({
+    transform() {
+      throw thrownError;
+    }
+  });
+
+  const reader = ts.readable.getReader();
+
+  const writer = ts.writable.getWriter();
+
+  return Promise.all([
+    promise_rejects_exactly(t, thrownError, writer.write('a'),
+                            'writable\'s write should reject with the thrown error'),
+    promise_rejects_exactly(t, thrownError, reader.read(),
+                            'readable\'s read should reject with the thrown error'),
+    promise_rejects_exactly(t, thrownError, reader.closed,
+                            'readable\'s closed should be rejected with the thrown error'),
+    promise_rejects_exactly(t, thrownError, writer.closed,
+                            'writable\'s closed should be rejected with the thrown error')
+  ]);
+}, 'TransformStream errors thrown in transform put the writable and readable in an errored state');
+
+promise_test(t => {
+  const ts = new TransformStream({
+    transform() {
+    },
+    flush() {
+      throw thrownError;
+    }
+  });
+
+  const reader = ts.readable.getReader();
+
+  const writer = ts.writable.getWriter();
+
+  return Promise.all([
+    writer.write('a'),
+    promise_rejects_exactly(t, thrownError, writer.close(),
+                            'writable\'s close should reject with the thrown error'),
+    promise_rejects_exactly(t, thrownError, reader.read(),
+                            'readable\'s read should reject with the thrown error'),
+    promise_rejects_exactly(t, thrownError, reader.closed,
+                            'readable\'s closed should be rejected with the thrown error'),
+    promise_rejects_exactly(t, thrownError, writer.closed,
+                            'writable\'s closed should be rejected with the thrown error')
+  ]);
+}, 'TransformStream errors thrown in flush put the writable and readable in an errored state');
+
+test(() => {
+  new TransformStream({
+    start(c) {
+      c.enqueue('a');
+      c.error(new Error('generic error'));
+      assert_throws_js(TypeError, () => c.enqueue('b'), 'enqueue() should throw');
+    }
+  });
+}, 'errored TransformStream should not enqueue new chunks');
+
+promise_test(t => {
+  const ts = new TransformStream({
+    start() {
+      return flushAsyncEvents().then(() => {
+        throw thrownError;
+      });
+    },
+    transform: t.unreached_func('transform should not be called'),
+    flush: t.unreached_func('flush should not be called')
+  });
+
+  const writer = ts.writable.getWriter();
+  const reader = ts.readable.getReader();
+  return Promise.all([
+    promise_rejects_exactly(t, thrownError, writer.write('a'), 'writer should reject with thrownError'),
+    promise_rejects_exactly(t, thrownError, writer.close(), 'close() should reject with thrownError'),
+    promise_rejects_exactly(t, thrownError, reader.read(), 'reader should reject with thrownError')
+  ]);
+}, 'TransformStream transformer.start() rejected promise should error the stream');
+
+promise_test(t => {
+  const controllerError = new Error('start failure');
+  controllerError.name = 'controllerError';
+  const ts = new TransformStream({
+    start(c) {
+      return flushAsyncEvents()
+        .then(() => {
+          c.error(controllerError);
+          throw new Error('ignored error');
+        });
+    },
+    transform: t.unreached_func('transform should never be called if start() fails'),
+    flush: t.unreached_func('flush should never be called if start() fails')
+  });
+
+  const writer = ts.writable.getWriter();
+  const reader = ts.readable.getReader();
+  return Promise.all([
+    promise_rejects_exactly(t, controllerError, writer.write('a'), 'writer should reject with controllerError'),
+    promise_rejects_exactly(t, controllerError, writer.close(), 'close should reject with same error'),
+    promise_rejects_exactly(t, controllerError, reader.read(), 'reader should reject with same error')
+  ]);
+}, 'when controller.error is followed by a rejection, the error reason should come from controller.error');
+
+test(() => {
+  assert_throws_js(URIError, () => new TransformStream({
+    start() { throw new URIError('start thrown error'); },
+    transform() {}
+  }), 'constructor should throw');
+}, 'TransformStream constructor should throw when start does');
+
+test(() => {
+  const strategy = {
+    size() { throw new URIError('size thrown error'); }
+  };
+
+  assert_throws_js(URIError, () => new TransformStream({
+    start(c) {
+      c.enqueue('a');
+    },
+    transform() {}
+  }, undefined, strategy), 'constructor should throw the same error strategy.size throws');
+}, 'when strategy.size throws inside start(), the constructor should throw the same error');
+
+test(() => {
+  const controllerError = new URIError('controller.error');
+
+  let controller;
+  const strategy = {
+    size() {
+      controller.error(controllerError);
+      throw new Error('redundant error');
+    }
+  };
+
+  assert_throws_js(URIError, () => new TransformStream({
+    start(c) {
+      controller = c;
+      c.enqueue('a');
+    },
+    transform() {}
+  }, undefined, strategy), 'the first error should be thrown');
+}, 'when strategy.size calls controller.error() then throws, the constructor should throw the first error');
+
+promise_test(t => {
+  const ts = new TransformStream();
+  const writer = ts.writable.getWriter();
+  const closedPromise = writer.closed;
+  return Promise.all([
+    ts.readable.cancel(thrownError),
+    promise_rejects_exactly(t, thrownError, closedPromise, 'closed should throw a TypeError')
+  ]);
+}, 'cancelling the readable side should error the writable');
+
+promise_test(t => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const writer = ts.writable.getWriter();
+  const reader = ts.readable.getReader();
+  const writePromise = writer.write('a');
+  const closePromise = writer.close();
+  controller.error(thrownError);
+  return Promise.all([
+    promise_rejects_exactly(t, thrownError, reader.closed, 'reader.closed should reject'),
+    promise_rejects_exactly(t, thrownError, writePromise, 'writePromise should reject'),
+    promise_rejects_exactly(t, thrownError, closePromise, 'closePromise should reject')]);
+}, 'it should be possible to error the readable between close requested and complete');
+
+promise_test(t => {
+  const ts = new TransformStream({
+    transform(chunk, controller) {
+      controller.enqueue(chunk);
+      controller.terminate();
+      throw thrownError;
+    }
+  }, undefined, { highWaterMark: 1 });
+  const writePromise = ts.writable.getWriter().write('a');
+  const closedPromise = ts.readable.getReader().closed;
+  return Promise.all([
+    promise_rejects_exactly(t, thrownError, writePromise, 'write() should reject'),
+    promise_rejects_exactly(t, thrownError, closedPromise, 'reader.closed should reject')
+  ]);
+}, 'an exception from transform() should error the stream if terminate has been requested but not completed');
+
+promise_test(t => {
+  const ts = new TransformStream();
+  const writer = ts.writable.getWriter();
+  // The microtask following transformer.start() hasn't completed yet, so the abort is queued and not notified to the
+  // TransformStream yet.
+  const abortPromise = writer.abort(thrownError);
+  const cancelPromise = ts.readable.cancel(new Error('cancel reason'));
+  return Promise.all([
+    abortPromise,
+    cancelPromise,
+    promise_rejects_exactly(t, thrownError, writer.closed, 'writer.closed should reject with thrownError')]);
+}, 'abort should set the close reason for the writable when it happens before cancel during start, but cancel should ' +
+             'still succeed');
+
+promise_test(t => {
+  let resolveTransform;
+  const transformPromise = new Promise(resolve => {
+    resolveTransform = resolve;
+  });
+  const ts = new TransformStream({
+    transform() {
+      return transformPromise;
+    }
+  }, undefined, { highWaterMark: 2 });
+  const writer = ts.writable.getWriter();
+  return delay(0).then(() => {
+    const writePromise = writer.write();
+    const abortPromise = writer.abort(thrownError);
+    const cancelPromise = ts.readable.cancel(new Error('cancel reason'));
+    resolveTransform();
+    return Promise.all([
+      writePromise,
+      abortPromise,
+      cancelPromise,
+      promise_rejects_exactly(t, thrownError, writer.closed, 'writer.closed should reject with thrownError')]);
+  });
+}, 'abort should set the close reason for the writable when it happens before cancel during underlying sink write, ' +
+             'but cancel should still succeed');
+
+const ignoredError = new Error('ignoredError');
+ignoredError.name = 'ignoredError';
+
+promise_test(t => {
+  const ts = new TransformStream({
+    start(controller) {
+      controller.error(thrownError);
+      controller.error(ignoredError);
+    }
+  });
+  return promise_rejects_exactly(t, thrownError, ts.writable.abort(), 'abort() should reject with thrownError');
+}, 'controller.error() should do nothing the second time it is called');
+
+promise_test(t => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const cancelPromise = ts.readable.cancel(thrownError);
+  controller.error(ignoredError);
+  return Promise.all([
+    cancelPromise,
+    promise_rejects_exactly(t, thrownError, ts.writable.getWriter().closed, 'closed should reject with thrownError')
+  ]);
+}, 'controller.error() should do nothing after readable.cancel()');
+
+promise_test(t => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  return ts.writable.abort(thrownError).then(() => {
+    controller.error(ignoredError);
+    return promise_rejects_exactly(t, thrownError, ts.writable.getWriter().closed, 'closed should reject with thrownError');
+  });
+}, 'controller.error() should do nothing after writable.abort() has completed');
+
+promise_test(t => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    },
+    transform() {
+      throw thrownError;
+    }
+  }, undefined, { highWaterMark: Infinity });
+  const writer = ts.writable.getWriter();
+  return promise_rejects_exactly(t, thrownError, writer.write(), 'write() should reject').then(() => {
+    controller.error();
+    return promise_rejects_exactly(t, thrownError, writer.closed, 'closed should reject with thrownError');
+  });
+}, 'controller.error() should do nothing after a transformer method has thrown an exception');
+
+promise_test(t => {
+  let controller;
+  let calls = 0;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    },
+    transform() {
+      ++calls;
+    }
+  }, undefined, { highWaterMark: 1 });
+  return delay(0).then(() => {
+    // Create backpressure.
+    controller.enqueue('a');
+    const writer = ts.writable.getWriter();
+    // transform() will not be called until backpressure is relieved.
+    const writePromise = writer.write('b');
+    assert_equals(calls, 0, 'transform() should not have been called');
+    controller.error(thrownError);
+    // Now backpressure has been relieved and the write can proceed.
+    return promise_rejects_exactly(t, thrownError, writePromise, 'write() should reject').then(() => {
+      assert_equals(calls, 0, 'transform() should not be called');
+    });
+  });
+}, 'erroring during write with backpressure should result in the write failing');
+
+promise_test(t => {
+  const ts = new TransformStream({}, undefined, { highWaterMark: 0 });
+  return delay(0).then(() => {
+    const writer = ts.writable.getWriter();
+    // write should start synchronously
+    const writePromise = writer.write(0);
+    // The underlying sink's abort() is not called until the write() completes.
+    const abortPromise = writer.abort(thrownError);
+    // Perform a read to relieve backpressure and permit the write() to complete.
+    const readPromise = ts.readable.getReader().read();
+    return Promise.all([
+      promise_rejects_exactly(t, thrownError, readPromise, 'read() should reject'),
+      promise_rejects_exactly(t, thrownError, writePromise, 'write() should reject'),
+      abortPromise
+    ]);
+  });
+}, 'a write() that was waiting for backpressure should reject if the writable is aborted');
+
+promise_test(t => {
+  const ts = new TransformStream();
+  ts.writable.abort(thrownError);
+  const reader = ts.readable.getReader();
+  return promise_rejects_exactly(t, thrownError, reader.read(), 'read() should reject with thrownError');
+}, 'the readable should be errored with the reason passed to the writable abort() method');
diff --git a/testing/web-platform/tests/streams/transform-streams/flush.any.js b/testing/web-platform/tests/streams/transform-streams/flush.any.js
new file mode 100644
index 0000000000..9287f6f5eb
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/flush.any.js
@@ -0,0 +1,131 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+'use strict';
+
+promise_test(() => {
+  let flushCalled = false;
+  const ts = new TransformStream({
+    transform() { },
+    flush() {
+      flushCalled = true;
+    }
+  });
+
+  return ts.writable.getWriter().close().then(() => {
+    return assert_true(flushCalled, 'closing the writable triggers the transform flush immediately');
+  });
+}, 'TransformStream flush is called immediately when the writable is closed, if no writes are queued');
+
+promise_test(() => {
+  let flushCalled = false;
+  let resolveTransform;
+  const ts = new TransformStream({
+    transform() {
+      return new Promise(resolve => {
+        resolveTransform = resolve;
+      });
+    },
+    flush() {
+      flushCalled = true;
+      return new Promise(() => {}); // never resolves
+    }
+  }, undefined, { highWaterMark: 1 });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+  assert_false(flushCalled, 'closing the writable does not immediately call flush if writes are not finished');
+
+  let rsClosed = false;
+  ts.readable.getReader().closed.then(() => {
+    rsClosed = true;
+  });
+
+  return delay(0).then(() => {
+    assert_false(flushCalled, 'closing the writable does not asynchronously call flush if writes are not finished');
+    resolveTransform();
+    return delay(0);
+  }).then(() => {
+    assert_true(flushCalled, 'flush is eventually called');
+    assert_false(rsClosed, 'if flushPromise does not resolve, the readable does not become closed');
+  });
+}, 'TransformStream flush is called after all queued writes finish, once the writable is closed');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform() {
+    },
+    flush() {
+      c.enqueue('x');
+      c.enqueue('y');
+    }
+  });
+
+  const reader = ts.readable.getReader();
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+  return reader.read().then(result1 => {
+    assert_equals(result1.value, 'x', 'the first chunk read is the first one enqueued in flush');
+    assert_equals(result1.done, false, 'the first chunk read is the first one enqueued in flush');
+
+    return reader.read().then(result2 => {
+      assert_equals(result2.value, 'y', 'the second chunk read is the second one enqueued in flush');
+      assert_equals(result2.done, false, 'the second chunk read is the second one enqueued in flush');
+    });
+  });
+}, 'TransformStream flush gets a chance to enqueue more into the readable');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform() {
+    },
+    flush() {
+      c.enqueue('x');
+      c.enqueue('y');
+      return delay(0);
+    }
+  });
+
+  const reader = ts.readable.getReader();
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+
+  return Promise.all([
+    reader.read().then(result1 => {
+      assert_equals(result1.value, 'x', 'the first chunk read is the first one enqueued in flush');
+      assert_equals(result1.done, false, 'the first chunk read is the first one enqueued in flush');
+
+      return reader.read().then(result2 => {
+        assert_equals(result2.value, 'y', 'the second chunk read is the second one enqueued in flush');
+        assert_equals(result2.done, false, 'the second chunk read is the second one enqueued in flush');
+      });
+    }),
+    reader.closed.then(() => {
+      assert_true(true, 'readable reader becomes closed');
+    })
+  ]);
+}, 'TransformStream flush gets a chance to enqueue more into the readable, and can then async close');
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+promise_test(t => {
+  const ts = new TransformStream({
+    flush(controller) {
+      controller.error(error1);
+    }
+  });
+  return promise_rejects_exactly(t, error1, ts.writable.getWriter().close(), 'close() should reject');
+}, 'error() during flush should cause writer.close() to reject');
diff --git a/testing/web-platform/tests/streams/transform-streams/general.any.js b/testing/web-platform/tests/streams/transform-streams/general.any.js
new file mode 100644
index 0000000000..c95691f7bf
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/general.any.js
@@ -0,0 +1,437 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+'use strict';
+
+test(() => {
+  new TransformStream({ transform() { } });
+}, 'TransformStream can be constructed with a transform function');
+
+test(() => {
+  new TransformStream();
+  new TransformStream({});
+}, 'TransformStream can be constructed with no transform function');
+
+test(() => {
+  const ts = new TransformStream({ transform() { } });
+
+  const writer = ts.writable.getWriter();
+  assert_equals(writer.desiredSize, 1, 'writer.desiredSize should be 1');
+}, 'TransformStream writable starts in the writable state');
+
+promise_test(() => {
+  const ts = new TransformStream();
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  assert_equals(writer.desiredSize, 0, 'writer.desiredSize should be 0 after write()');
+
+  return ts.readable.getReader().read().then(result => {
+    assert_equals(result.value, 'a',
+      'result from reading the readable is the same as was written to writable');
+    assert_false(result.done, 'stream should not be done');
+
+    return delay(0).then(() => assert_equals(writer.desiredSize, 1, 'desiredSize should be 1 again'));
+  });
+}, 'Identity TransformStream: can read from readable what is put into writable');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform(chunk) {
+      c.enqueue(chunk.toUpperCase());
+    }
+  });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+
+  return ts.readable.getReader().read().then(result => {
+    assert_equals(result.value, 'A',
+      'result from reading the readable is the transformation of what was written to writable');
+    assert_false(result.done, 'stream should not be done');
+  });
+}, 'Uppercaser sync TransformStream: can read from readable transformed version of what is put into writable');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform(chunk) {
+      c.enqueue(chunk.toUpperCase());
+      c.enqueue(chunk.toUpperCase());
+    }
+  });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+
+  const reader = ts.readable.getReader();
+
+  return reader.read().then(result1 => {
+    assert_equals(result1.value, 'A',
+      'the first chunk read is the transformation of the single chunk written');
+    assert_false(result1.done, 'stream should not be done');
+
+    return reader.read().then(result2 => {
+      assert_equals(result2.value, 'A',
+        'the second chunk read is also the transformation of the single chunk written');
+      assert_false(result2.done, 'stream should not be done');
+    });
+  });
+}, 'Uppercaser-doubler sync TransformStream: can read both chunks put into the readable');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform(chunk) {
+      return delay(0).then(() => c.enqueue(chunk.toUpperCase()));
+    }
+  });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+
+  return ts.readable.getReader().read().then(result => {
+    assert_equals(result.value, 'A',
+      'result from reading the readable is the transformation of what was written to writable');
+    assert_false(result.done, 'stream should not be done');
+  });
+}, 'Uppercaser async TransformStream: can read from readable transformed version of what is put into writable');
+
+promise_test(() => {
+  let doSecondEnqueue;
+  let returnFromTransform;
+  const ts = new TransformStream({
+    transform(chunk, controller) {
+      delay(0).then(() => controller.enqueue(chunk.toUpperCase()));
+      doSecondEnqueue = () => controller.enqueue(chunk.toUpperCase());
+      return new Promise(resolve => {
+        returnFromTransform = resolve;
+      });
+    }
+  });
+
+  const reader = ts.readable.getReader();
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+
+  return reader.read().then(result1 => {
+    assert_equals(result1.value, 'A',
+      'the first chunk read is the transformation of the single chunk written');
+    assert_false(result1.done, 'stream should not be done');
+    doSecondEnqueue();
+
+    return reader.read().then(result2 => {
+      assert_equals(result2.value, 'A',
+        'the second chunk read is also the transformation of the single chunk written');
+      assert_false(result2.done, 'stream should not be done');
+      returnFromTransform();
+    });
+  });
+}, 'Uppercaser-doubler async TransformStream: can read both chunks put into the readable');
+
+promise_test(() => {
+  const ts = new TransformStream({ transform() { } });
+
+  const writer = ts.writable.getWriter();
+  writer.close();
+
+  return Promise.all([writer.closed, ts.readable.getReader().closed]);
+}, 'TransformStream: by default, closing the writable closes the readable (when there are no queued writes)');
+
+promise_test(() => {
+  let transformResolve;
+  const transformPromise = new Promise(resolve => {
+    transformResolve = resolve;
+  });
+  const ts = new TransformStream({
+    transform() {
+      return transformPromise;
+    }
+  }, undefined, { highWaterMark: 1 });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+
+  let rsClosed = false;
+  ts.readable.getReader().closed.then(() => {
+    rsClosed = true;
+  });
+
+  return delay(0).then(() => {
+    assert_equals(rsClosed, false, 'readable is not closed after a tick');
+    transformResolve();
+
+    return writer.closed.then(() => {
+      // TODO: Is this expectation correct?
+      assert_equals(rsClosed, true, 'readable is closed at that point');
+    });
+  });
+}, 'TransformStream: by default, closing the writable waits for transforms to finish before closing both');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform() {
+      c.enqueue('x');
+      c.enqueue('y');
+      return delay(0);
+    }
+  });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+
+  const readableChunks = readableStreamToArray(ts.readable);
+
+  return writer.closed.then(() => {
+    return readableChunks.then(chunks => {
+      assert_array_equals(chunks, ['x', 'y'], 'both enqueued chunks can be read from the readable');
+    });
+  });
+}, 'TransformStream: by default, closing the writable closes the readable after sync enqueues and async done');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    start(controller) {
+      c = controller;
+    },
+    transform() {
+      return delay(0)
+          .then(() => c.enqueue('x'))
+          .then(() => c.enqueue('y'))
+          .then(() => delay(0));
+    }
+  });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+
+  const readableChunks = readableStreamToArray(ts.readable);
+
+  return writer.closed.then(() => {
+    return readableChunks.then(chunks => {
+      assert_array_equals(chunks, ['x', 'y'], 'both enqueued chunks can be read from the readable');
+    });
+  });
+}, 'TransformStream: by default, closing the writable closes the readable after async enqueues and async done');
+
+promise_test(() => {
+  let c;
+  const ts = new TransformStream({
+    suffix: '-suffix',
+
+    start(controller) {
+      c = controller;
+      c.enqueue('start' + this.suffix);
+    },
+
+    transform(chunk) {
+      c.enqueue(chunk + this.suffix);
+    },
+
+    flush() {
+      c.enqueue('flushed' + this.suffix);
+    }
+  });
+
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+
+  const readableChunks = readableStreamToArray(ts.readable);
+
+  return writer.closed.then(() => {
+    return readableChunks.then(chunks => {
+      assert_array_equals(chunks, ['start-suffix', 'a-suffix', 'flushed-suffix'], 'all enqueued chunks have suffixes');
+    });
+  });
+}, 'Transform stream should call transformer methods as methods');
+
+promise_test(() => {
+  function functionWithOverloads() {}
+  functionWithOverloads.apply = () => assert_unreached('apply() should not be called');
+  functionWithOverloads.call = () => assert_unreached('call() should not be called');
+  const ts = new TransformStream({
+    start: functionWithOverloads,
+    transform: functionWithOverloads,
+    flush: functionWithOverloads
+  });
+  const writer = ts.writable.getWriter();
+  writer.write('a');
+  writer.close();
+
+  return readableStreamToArray(ts.readable);
+}, 'methods should not not have .apply() or .call() called');
+
+promise_test(t => {
+  let startCalled = false;
+  let startDone = false;
+  let transformDone = false;
+  let flushDone = false;
+  const ts = new TransformStream({
+    start() {
+      startCalled = true;
+      return flushAsyncEvents().then(() => {
+        startDone = true;
+      });
+    },
+    transform() {
+      return t.step(() => {
+        assert_true(startDone, 'transform() should not be called until the promise returned from start() has resolved');
+        return flushAsyncEvents().then(() => {
+          transformDone = true;
+        });
+      });
+    },
+    flush() {
+      return t.step(() => {
+        assert_true(transformDone,
+                    'flush() should not be called until the promise returned from transform() has resolved');
+        return flushAsyncEvents().then(() => {
+          flushDone = true;
+        });
+      });
+    }
+  }, undefined, { highWaterMark: 1 });
+
+  assert_true(startCalled, 'start() should be called synchronously');
+
+  const writer = ts.writable.getWriter();
+  const writePromise = writer.write('a');
+  return writer.close().then(() => {
+    assert_true(flushDone, 'promise returned from flush() should have resolved');
+    return writePromise;
+  });
+}, 'TransformStream start, transform, and flush should be strictly ordered');
+
+promise_test(() => {
+  let transformCalled = false;
+  const ts = new TransformStream({
+    transform() {
+      transformCalled = true;
+    }
+  }, undefined, { highWaterMark: Infinity });
+  // transform() is only called synchronously when there is no backpressure and all microtasks have run.
+  return delay(0).then(() => {
+    const writePromise = ts.writable.getWriter().write();
+    assert_true(transformCalled, 'transform() should have been called');
+    return writePromise;
+  });
+}, 'it should be possible to call transform() synchronously');
+
+promise_test(() => {
+  const ts = new TransformStream({}, undefined, { highWaterMark: 0 });
+
+  const writer = ts.writable.getWriter();
+  writer.close();
+
+  return Promise.all([writer.closed, ts.readable.getReader().closed]);
+}, 'closing the writable should close the readable when there are no queued chunks, even with backpressure');
+
+test(() => {
+  new TransformStream({
+    start(controller) {
+      controller.terminate();
+      assert_throws_js(TypeError, () => controller.enqueue(), 'enqueue should throw');
+    }
+  });
+}, 'enqueue() should throw after controller.terminate()');
+
+promise_test(() => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const cancelPromise = ts.readable.cancel();
+  assert_throws_js(TypeError, () => controller.enqueue(), 'enqueue should throw');
+  return cancelPromise;
+}, 'enqueue() should throw after readable.cancel()');
+
+test(() => {
+  new TransformStream({
+    start(controller) {
+      controller.terminate();
+      controller.terminate();
+    }
+  });
+}, 'controller.terminate() should do nothing the second time it is called');
+
+promise_test(t => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  const cancelReason = { name: 'cancelReason' };
+  const cancelPromise = ts.readable.cancel(cancelReason);
+  controller.terminate();
+  return Promise.all([
+    cancelPromise,
+    promise_rejects_exactly(t, cancelReason, ts.writable.getWriter().closed, 'closed should reject with cancelReason')
+  ]);
+}, 'terminate() should do nothing after readable.cancel()');
+
+promise_test(() => {
+  let calls = 0;
+  new TransformStream({
+    start() {
+      ++calls;
+    }
+  });
+  return flushAsyncEvents().then(() => {
+    assert_equals(calls, 1, 'start() should have been called exactly once');
+  });
+}, 'start() should not be called twice');
+
+test(() => {
+  assert_throws_js(RangeError, () => new TransformStream({ readableType: 'bytes' }), 'constructor should throw');
+}, 'specifying a defined readableType should throw');
+
+test(() => {
+  assert_throws_js(RangeError, () => new TransformStream({ writableType: 'bytes' }), 'constructor should throw');
+}, 'specifying a defined writableType should throw');
+
+test(() => {
+  class Subclass extends TransformStream {
+    extraFunction() {
+      return true;
+    }
+  }
+  assert_equals(
+      Object.getPrototypeOf(Subclass.prototype), TransformStream.prototype,
+      'Subclass.prototype\'s prototype should be TransformStream.prototype');
+  assert_equals(Object.getPrototypeOf(Subclass), TransformStream,
+                'Subclass\'s prototype should be TransformStream');
+  const sub = new Subclass();
+  assert_true(sub instanceof TransformStream,
+              'Subclass object should be an instance of TransformStream');
+  assert_true(sub instanceof Subclass,
+              'Subclass object should be an instance of Subclass');
+  const readableGetter = Object.getOwnPropertyDescriptor(
+      TransformStream.prototype, 'readable').get;
+  assert_equals(readableGetter.call(sub), sub.readable,
+                'Subclass object should pass brand check');
+  assert_true(sub.extraFunction(),
+              'extraFunction() should be present on Subclass object');
+}, 'Subclassing TransformStream should work');
diff --git a/testing/web-platform/tests/streams/transform-streams/invalid-realm.tentative.window.js b/testing/web-platform/tests/streams/transform-streams/invalid-realm.tentative.window.js
new file mode 100644
index 0000000000..57cdfd9486
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/invalid-realm.tentative.window.js
@@ -0,0 +1,17 @@
+// TransformStream should still work even if the realm is detached.
+
+// Adds an iframe to the document and returns it.
+function addIframe() {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+  return iframe;
+}
+
+promise_test(async t => {
+  const iframe = addIframe();
+  const stream = new iframe.contentWindow.TransformStream();
+  const readPromise = stream.readable.getReader().read();
+  const writer = stream.writable.getWriter();
+  iframe.remove();
+  return Promise.all([writer.write('A'), readPromise]);
+}, 'TransformStream: write in detached realm should succeed');
diff --git a/testing/web-platform/tests/streams/transform-streams/lipfuzz.any.js b/testing/web-platform/tests/streams/transform-streams/lipfuzz.any.js
new file mode 100644
index 0000000000..f9f148aaf1
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/lipfuzz.any.js
@@ -0,0 +1,163 @@
+// META: global=window,worker
+'use strict';
+
+class LipFuzzTransformer {
+  constructor(substitutions) {
+    this.substitutions = substitutions;
+    this.partialChunk = '';
+    this.lastIndex = undefined;
+  }
+
+  transform(chunk, controller) {
+    chunk = this.partialChunk + chunk;
+    this.partialChunk = '';
+    // lastIndex is the index of the first character after the last substitution.
+    this.lastIndex = 0;
+    chunk = chunk.replace(/\{\{([a-zA-Z0-9_-]+)\}\}/g, this.replaceTag.bind(this));
+    // Regular expression for an incomplete template at the end of a string.
+    const partialAtEndRegexp = /\{(\{([a-zA-Z0-9_-]+(\})?)?)?$/g;
+    // Avoid looking at any characters that have already been substituted.
+    partialAtEndRegexp.lastIndex = this.lastIndex;
+    this.lastIndex = undefined;
+    const match = partialAtEndRegexp.exec(chunk);
+    if (match) {
+      this.partialChunk = chunk.substring(match.index);
+      chunk = chunk.substring(0, match.index);
+    }
+    controller.enqueue(chunk);
+  }
+
+  flush(controller) {
+    if (this.partialChunk.length > 0) {
+      controller.enqueue(this.partialChunk);
+    }
+  }
+
+  replaceTag(match, p1, offset) {
+    let replacement = this.substitutions[p1];
+    if (replacement === undefined) {
+      replacement = '';
+    }
+    this.lastIndex = offset + replacement.length;
+    return replacement;
+  }
+}
+
+const substitutions = {
+  in1: 'out1',
+  in2: 'out2',
+  quine: '{{quine}}',
+  bogusPartial: '{{incompleteResult}'
+};
+
+const cases = [
+  {
+    input: [''],
+    output: ['']
+  },
+  {
+    input: [],
+    output: []
+  },
+  {
+    input: ['{{in1}}'],
+    output: ['out1']
+  },
+  {
+    input: ['z{{in1}}'],
+    output: ['zout1']
+  },
+  {
+    input: ['{{in1}}q'],
+    output: ['out1q']
+  },
+  {
+    input: ['{{in1}}{{in1}'],
+    output: ['out1', '{{in1}']
+  },
+  {
+    input: ['{{in1}}{{in1}', '}'],
+    output: ['out1', 'out1']
+  },
+  {
+    input: ['{{in1', '}}'],
+    output: ['', 'out1']
+  },
+  {
+    input: ['{{', 'in1}}'],
+    output: ['', 'out1']
+  },
+  {
+    input: ['{', '{in1}}'],
+    output: ['', 'out1']
+  },
+  {
+    input: ['{{', 'in1}'],
+    output: ['', '', '{{in1}']
+  },
+  {
+    input: ['{'],
+    output: ['', '{']
+  },
+  {
+    input: ['{', ''],
+    output: ['', '', '{']
+  },
+  {
+    input: ['{', '{', 'i', 'n', '1', '}', '}'],
+    output: ['', '', '', '', '', '', 'out1']
+  },
+  {
+    input: ['{{in1}}{{in2}}{{in1}}'],
+    output: ['out1out2out1']
+  },
+  {
+    input: ['{{wrong}}'],
+    output: ['']
+  },
+  {
+    input: ['{{wron', 'g}}'],
+    output: ['', '']
+  },
+  {
+    input: ['{{quine}}'],
+    output: ['{{quine}}']
+  },
+  {
+    input: ['{{bogusPartial}}'],
+    output: ['{{incompleteResult}']
+  },
+  {
+    input: ['{{bogusPartial}}}'],
+    output: ['{{incompleteResult}}']
+  }
+];
+
+for (const testCase of cases) {
+  const inputChunks = testCase.input;
+  const outputChunks = testCase.output;
+  promise_test(() => {
+    const lft = new TransformStream(new LipFuzzTransformer(substitutions));
+    const writer = lft.writable.getWriter();
+    const promises = [];
+    for (const inputChunk of inputChunks) {
+      promises.push(writer.write(inputChunk));
+    }
+    promises.push(writer.close());
+    const reader = lft.readable.getReader();
+    let readerChain = Promise.resolve();
+    for (const outputChunk of outputChunks) {
+      readerChain = readerChain.then(() => {
+        return reader.read().then(({ value, done }) => {
+          assert_false(done, `done should be false when reading ${outputChunk}`);
+          assert_equals(value, outputChunk, `value should match outputChunk`);
+        });
+      });
+    }
+    readerChain = readerChain.then(() => {
+      return reader.read().then(({ done }) => assert_true(done, `done should be true`));
+    });
+    promises.push(readerChain);
+    return Promise.all(promises);
+  }, `testing "${inputChunks}" (length ${inputChunks.length})`);
+}
diff --git a/testing/web-platform/tests/streams/transform-streams/patched-global.any.js b/testing/web-platform/tests/streams/transform-streams/patched-global.any.js
new file mode 100644
index 0000000000..2d04e3b948
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/patched-global.any.js
@@ -0,0 +1,53 @@
+// META: global=window,worker
+'use strict';
+
+// Tests which patch the global environment are kept separate to avoid
+// interfering with other tests.
+
+test(t => {
+  // eslint-disable-next-line no-extend-native, accessor-pairs
+  Object.defineProperty(Object.prototype, 'highWaterMark', {
+    set() { throw new Error('highWaterMark setter called'); },
+    configurable: true
+  });
+
+  // eslint-disable-next-line no-extend-native, accessor-pairs
+  Object.defineProperty(Object.prototype, 'size', {
+    set() { throw new Error('size setter called'); },
+    configurable: true
+  });
+
+  t.add_cleanup(() => {
+    delete Object.prototype.highWaterMark;
+    delete Object.prototype.size;
+  });
+
+  assert_not_equals(new TransformStream(), null, 'constructor should work');
+}, 'TransformStream constructor should not call setters for highWaterMark or size');
+
+test(t => {
+  const oldReadableStream = ReadableStream;
+  const oldWritableStream = WritableStream;
+  const getReader = ReadableStream.prototype.getReader;
+  const getWriter = WritableStream.prototype.getWriter;
+
+  // Replace ReadableStream and WritableStream with broken versions.
+  ReadableStream = function () {
+    throw new Error('Called the global ReadableStream constructor');
+  };
+  WritableStream = function () {
+    throw new Error('Called the global WritableStream constructor');
+  };
+  t.add_cleanup(() => {
+    ReadableStream = oldReadableStream;
+    WritableStream = oldWritableStream;
+  });
+
+  const ts = new TransformStream();
+
+  // Just to be sure, ensure the readable and writable pass brand checks.
+  assert_not_equals(getReader.call(ts.readable), undefined,
+                    'getReader should work when called on ts.readable');
+  assert_not_equals(getWriter.call(ts.writable), undefined,
+                    'getWriter should work when called on ts.writable');
+}, 'TransformStream should use the original value of ReadableStream and WritableStream');
diff --git a/testing/web-platform/tests/streams/transform-streams/properties.any.js b/testing/web-platform/tests/streams/transform-streams/properties.any.js
new file mode 100644
index 0000000000..02981b8bc7
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/properties.any.js
@@ -0,0 +1,49 @@
+// META: global=window,worker
+'use strict';
+
+const transformerMethods = {
+  start: {
+    length: 1,
+    trigger: () => Promise.resolve()
+  },
+  transform: {
+    length: 2,
+    trigger: ts => ts.writable.getWriter().write()
+  },
+  flush: {
+    length: 1,
+    trigger: ts => ts.writable.getWriter().close()
+  }
+};
+
+for (const method in transformerMethods) {
+  const { length, trigger } = transformerMethods[method];
+
+  // Some semantic tests of how transformer methods are called can be found in general.js, as well as in the test files
+  // specific to each method.
+  promise_test(() => {
+    let argCount;
+    const ts = new TransformStream({
+      [method](...args) {
+        argCount = args.length;
+      }
+    }, undefined, { highWaterMark: Infinity });
+    return Promise.resolve(trigger(ts)).then(() => {
+      assert_equals(argCount, length, `${method} should be called with ${length} arguments`);
+    });
+  }, `transformer method ${method} should be called with the right number of arguments`);
+
+  promise_test(() => {
+    let methodWasCalled = false;
+    function Transformer() {}
+    Transformer.prototype = {
+      [method]() {
+        methodWasCalled = true;
+      }
+    };
+    const ts = new TransformStream(new Transformer(), undefined, { highWaterMark: Infinity });
+    return Promise.resolve(trigger(ts)).then(() => {
+      assert_true(methodWasCalled, `${method} should be called`);
+    });
+  }, `transformer method ${method} should be called even when it's located on the prototype chain`);
+}
diff --git a/testing/web-platform/tests/streams/transform-streams/reentrant-strategies.any.js b/testing/web-platform/tests/streams/transform-streams/reentrant-strategies.any.js
new file mode 100644
index 0000000000..fc2f918866
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/reentrant-strategies.any.js
@@ -0,0 +1,319 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+// The size() function of readableStrategy can re-entrantly call back into the TransformStream implementation. This
+// makes it risky to cache state across the call to ReadableStreamDefaultControllerEnqueue. These tests attempt to catch
+// such errors. They are separated from the other strategy tests because no real user code should ever do anything like
+// this.
+//
+// There is no such issue with writableStrategy size() because it is never called from within TransformStream
+// algorithms.
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+promise_test(() => {
+  let controller;
+  let calls = 0;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      ++calls;
+      if (calls < 2) {
+        controller.enqueue('b');
+      }
+      return 1;
+    },
+    highWaterMark: Infinity
+  });
+  const writer = ts.writable.getWriter();
+  return Promise.all([writer.write('a'), writer.close()])
+      .then(() => readableStreamToArray(ts.readable))
+      .then(array => assert_array_equals(array, ['b', 'a'], 'array should contain two chunks'));
+}, 'enqueue() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      // The readable queue is empty.
+      controller.terminate();
+      // The readable state has gone from "readable" to "closed".
+      return 1;
+      // This chunk will be enqueued, but will be impossible to read because the state is already "closed".
+    },
+    highWaterMark: Infinity
+  });
+  const writer = ts.writable.getWriter();
+  return writer.write('a')
+      .then(() => readableStreamToArray(ts.readable))
+      .then(array => assert_array_equals(array, [], 'array should contain no chunks'));
+  // The chunk 'a' is still in readable's queue. readable is closed so 'a' cannot be read. writable's queue is empty and
+  // it is still writable.
+}, 'terminate() inside size() should work');
+
+promise_test(t => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      controller.error(error1);
+      return 1;
+    },
+    highWaterMark: Infinity
+  });
+  const writer = ts.writable.getWriter();
+  return writer.write('a')
+      .then(() => promise_rejects_exactly(t, error1, ts.readable.getReader().read(), 'read() should reject'));
+}, 'error() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      assert_equals(controller.desiredSize, 1, 'desiredSize should be 1');
+      return 1;
+    },
+    highWaterMark: 1
+  });
+  const writer = ts.writable.getWriter();
+  return Promise.all([writer.write('a'), writer.close()])
+      .then(() => readableStreamToArray(ts.readable))
+      .then(array => assert_array_equals(array, ['a'], 'array should contain one chunk'));
+}, 'desiredSize inside size() should work');
+
+promise_test(t => {
+  let cancelPromise;
+  const ts = new TransformStream({}, undefined, {
+    size() {
+      cancelPromise = ts.readable.cancel(error1);
+      return 1;
+    },
+    highWaterMark: Infinity
+  });
+  const writer = ts.writable.getWriter();
+  return writer.write('a')
+      .then(() => {
+        promise_rejects_exactly(t, error1, writer.closed, 'writer.closed should reject');
+        return cancelPromise;
+      });
+}, 'readable cancel() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  let pipeToPromise;
+  const ws = recordingWritableStream();
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      if (!pipeToPromise) {
+        pipeToPromise = ts.readable.pipeTo(ws);
+      }
+      return 1;
+    },
+    highWaterMark: 1
+  });
+  // Allow promise returned by start() to resolve so that enqueue() will happen synchronously.
+  return delay(0).then(() => {
+    controller.enqueue('a');
+    assert_not_equals(pipeToPromise, undefined);
+
+    // Some pipeTo() implementations need an additional chunk enqueued in order for the first one to be processed. See
+    // https://github.com/whatwg/streams/issues/794 for background.
+    controller.enqueue('a');
+
+    // Give pipeTo() a chance to process the queued chunks.
+    return delay(0);
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'a'], 'ws should contain two chunks');
+    controller.terminate();
+    return pipeToPromise;
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'a', 'close'], 'target should have been closed');
+  });
+}, 'pipeTo() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  let readPromise;
+  let calls = 0;
+  let reader;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      // This is triggered by controller.enqueue(). The queue is empty and there are no pending reads. pull() is called
+      // synchronously, allowing transform() to proceed asynchronously. This results in a second call to enqueue(),
+      // which resolves this pending read() without calling size() again.
+      readPromise = reader.read();
+      ++calls;
+      return 1;
+    },
+    highWaterMark: 0
+  });
+  reader = ts.readable.getReader();
+  const writer = ts.writable.getWriter();
+  let writeResolved = false;
+  const writePromise = writer.write('b').then(() => {
+    writeResolved = true;
+  });
+  return flushAsyncEvents().then(() => {
+    assert_false(writeResolved);
+    controller.enqueue('a');
+    assert_equals(calls, 1, 'size() should have been called once');
+    return delay(0);
+  }).then(() => {
+    assert_true(writeResolved);
+    assert_equals(calls, 1, 'size() should only be called once');
+    return readPromise;
+  }).then(({ value, done }) => {
+    assert_false(done, 'done should be false');
+    // See https://github.com/whatwg/streams/issues/794 for why this chunk is not 'a'.
+    assert_equals(value, 'b', 'chunk should have been read');
+    assert_equals(calls, 1, 'calls should still be 1');
+    return writePromise;
+  });
+}, 'read() inside of size() should work');
+
+promise_test(() => {
+  let writer;
+  let writePromise1;
+  let calls = 0;
+  const ts = new TransformStream({}, undefined, {
+    size() {
+      ++calls;
+      if (calls < 2) {
+        writePromise1 = writer.write('a');
+      }
+      return 1;
+    },
+    highWaterMark: Infinity
+  });
+  writer = ts.writable.getWriter();
+  // Give pull() a chance to be called.
+  return delay(0).then(() => {
+    // This write results in a synchronous call to transform(), enqueue(), and size().
+    const writePromise2 = writer.write('b');
+    assert_equals(calls, 1, 'size() should have been called once');
+    return Promise.all([writePromise1, writePromise2, writer.close()]);
+  }).then(() => {
+    assert_equals(calls, 2, 'size() should have been called twice');
+    return readableStreamToArray(ts.readable);
+  }).then(array => {
+    assert_array_equals(array, ['b', 'a'], 'both chunks should have been enqueued');
+    assert_equals(calls, 2, 'calls should still be 2');
+  });
+}, 'writer.write() inside size() should work');
+
+promise_test(() => {
+  let controller;
+  let writer;
+  let writePromise;
+  let calls = 0;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      ++calls;
+      if (calls < 2) {
+        writePromise = writer.write('a');
+      }
+      return 1;
+    },
+    highWaterMark: Infinity
+  });
+  writer = ts.writable.getWriter();
+  // Give pull() a chance to be called.
+  return delay(0).then(() => {
+    // This enqueue results in synchronous calls to size(), write(), transform() and enqueue().
+    controller.enqueue('b');
+    assert_equals(calls, 2, 'size() should have been called twice');
+    return Promise.all([writePromise, writer.close()]);
+  }).then(() => {
+    return readableStreamToArray(ts.readable);
+  }).then(array => {
+    // Because one call to enqueue() is nested inside the other, they finish in the opposite order that they were
+    // called, so the chunks end up reverse order.
+    assert_array_equals(array, ['a', 'b'], 'both chunks should have been enqueued');
+    assert_equals(calls, 2, 'calls should still be 2');
+  });
+}, 'synchronous writer.write() inside size() should work');
+
+promise_test(() => {
+  let writer;
+  let closePromise;
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      closePromise = writer.close();
+      return 1;
+    },
+    highWaterMark: 1
+  });
+  writer = ts.writable.getWriter();
+  const reader = ts.readable.getReader();
+  // Wait for the promise returned by start() to be resolved so that the call to close() will result in a synchronous
+  // call to TransformStreamDefaultSink.
+  return delay(0).then(() => {
+    controller.enqueue('a');
+    return reader.read();
+  }).then(({ value, done }) => {
+    assert_false(done, 'done should be false');
+    assert_equals(value, 'a', 'value should be correct');
+    return reader.read();
+  }).then(({ done }) => {
+    assert_true(done, 'done should be true');
+    return closePromise;
+  });
+}, 'writer.close() inside size() should work');
+
+promise_test(t => {
+  let abortPromise;
+  let controller;
+  const ts = new TransformStream({
+    start(c) {
+      controller = c;
+    }
+  }, undefined, {
+    size() {
+      abortPromise = ts.writable.abort(error1);
+      return 1;
+    },
+    highWaterMark: 1
+  });
+  const reader = ts.readable.getReader();
+  // Wait for the promise returned by start() to be resolved so that the call to abort() will result in a synchronous
+  // call to TransformStreamDefaultSink.
+  return delay(0).then(() => {
+    controller.enqueue('a');
+    return Promise.all([promise_rejects_exactly(t, error1, reader.read(), 'read() should reject'), abortPromise]);
+  });
+}, 'writer.abort() inside size() should work');
diff --git a/testing/web-platform/tests/streams/transform-streams/strategies.any.js b/testing/web-platform/tests/streams/transform-streams/strategies.any.js
new file mode 100644
index 0000000000..94055ad99d
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/strategies.any.js
@@ -0,0 +1,150 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+// Here we just test that the strategies are correctly passed to the readable and writable sides. We assume that
+// ReadableStream and WritableStream will correctly apply the strategies when they are being used by a TransformStream
+// and so it isn't necessary to repeat their tests here.
+
+test(() => {
+  const ts = new TransformStream({}, { highWaterMark: 17 });
+  assert_equals(ts.writable.getWriter().desiredSize, 17, 'desiredSize should be 17');
+}, 'writableStrategy highWaterMark should work');
+
+promise_test(() => {
+  const ts = recordingTransformStream({}, undefined, { highWaterMark: 9 });
+  const writer = ts.writable.getWriter();
+  for (let i = 0; i < 10; ++i) {
+    writer.write(i);
+  }
+  return delay(0).then(() => {
+    assert_array_equals(ts.events, [
+      'transform', 0, 'transform', 1, 'transform', 2, 'transform', 3, 'transform', 4,
+      'transform', 5, 'transform', 6, 'transform', 7, 'transform', 8],
+                        'transform() should have been called 9 times');
+  });
+}, 'readableStrategy highWaterMark should work');
+
+promise_test(t => {
+  let writableSizeCalled = false;
+  let readableSizeCalled = false;
+  let transformCalled = false;
+  const ts = new TransformStream(
+    {
+      transform(chunk, controller) {
+        t.step(() => {
+          transformCalled = true;
+          assert_true(writableSizeCalled, 'writableStrategy.size() should have been called');
+          assert_false(readableSizeCalled, 'readableStrategy.size() should not have been called');
+          controller.enqueue(chunk);
+          assert_true(readableSizeCalled, 'readableStrategy.size() should have been called');
+        });
+      }
+    },
+    {
+      size() {
+        writableSizeCalled = true;
+        return 1;
+      }
+    },
+    {
+      size() {
+        readableSizeCalled = true;
+        return 1;
+      },
+      highWaterMark: Infinity
+    });
+  return ts.writable.getWriter().write().then(() => {
+    assert_true(transformCalled, 'transform() should be called');
+  });
+}, 'writable should have the correct size() function');
+
+test(() => {
+  const ts = new TransformStream();
+  const writer = ts.writable.getWriter();
+  assert_equals(writer.desiredSize, 1, 'default writable HWM is 1');
+  writer.write(undefined);
+  assert_equals(writer.desiredSize, 0, 'default chunk size is 1');
+}, 'default writable strategy should be equivalent to { highWaterMark: 1 }');
+
+promise_test(t => {
+  const ts = new TransformStream({
+    transform(chunk, controller) {
+      return t.step(() => {
+        assert_equals(controller.desiredSize, 0, 'desiredSize should be 0');
+        controller.enqueue(undefined);
+        // The first chunk enqueued is consumed by the pending read().
+        assert_equals(controller.desiredSize, 0, 'desiredSize should still be 0');
+        controller.enqueue(undefined);
+        assert_equals(controller.desiredSize, -1, 'desiredSize should be -1');
+      });
+    }
+  });
+  const writePromise = ts.writable.getWriter().write();
+  return ts.readable.getReader().read().then(() => writePromise);
+}, 'default readable strategy should be equivalent to { highWaterMark: 0 }');
+
+test(() => {
+  assert_throws_js(RangeError, () => new TransformStream(undefined, { highWaterMark: -1 }),
+                   'should throw RangeError for negative writableHighWaterMark');
+  assert_throws_js(RangeError, () => new TransformStream(undefined, undefined, { highWaterMark: -1 }),
+                   'should throw RangeError for negative readableHighWaterMark');
+  assert_throws_js(RangeError, () => new TransformStream(undefined, { highWaterMark: NaN }),
+                   'should throw RangeError for NaN writableHighWaterMark');
+  assert_throws_js(RangeError, () => new TransformStream(undefined, undefined, { highWaterMark: NaN }),
+                   'should throw RangeError for NaN readableHighWaterMark');
+}, 'a RangeError should be thrown for an invalid highWaterMark');
+
+const objectThatConvertsTo42 = {
+  toString() {
+    return '42';
+  }
+};
+
+test(() => {
+  const ts = new TransformStream(undefined, { highWaterMark: objectThatConvertsTo42 });
+  const writer = ts.writable.getWriter();
+  assert_equals(writer.desiredSize, 42, 'writable HWM is 42');
+}, 'writableStrategy highWaterMark should be converted to a number');
+
+test(() => {
+  const ts = new TransformStream({
+    start(controller) {
+      assert_equals(controller.desiredSize, 42, 'desiredSize should be 42');
+    }
+  }, undefined, { highWaterMark: objectThatConvertsTo42 });
+}, 'readableStrategy highWaterMark should be converted to a number');
+
+promise_test(t => {
+  const ts = new TransformStream(undefined, undefined, {
+    size() { return NaN; },
+    highWaterMark: 1
+  });
+  const writer = ts.writable.getWriter();
+  return promise_rejects_js(t, RangeError, writer.write(), 'write should reject');
+}, 'a bad readableStrategy size function should cause writer.write() to reject on an identity transform');
+
+promise_test(t => {
+  const ts = new TransformStream({
+    transform(chunk, controller) {
+      // This assert has the important side-effect of catching the error, so transform() does not throw.
+      assert_throws_js(RangeError, () => controller.enqueue(chunk), 'enqueue should throw');
+    }
+  }, undefined, {
+    size() {
+      return -1;
+    },
+    highWaterMark: 1
+  });
+
+  const writer = ts.writable.getWriter();
+  return writer.write().then(() => {
+    return Promise.all([
+      promise_rejects_js(t, RangeError, writer.ready, 'ready should reject'),
+      promise_rejects_js(t, RangeError, writer.closed, 'closed should reject'),
+      promise_rejects_js(t, RangeError, ts.readable.getReader().closed, 'readable closed should reject')
+    ]);
+  });
+}, 'a bad readableStrategy size function should error the stream on enqueue even when transformer.transform() ' +
+   'catches the exception');
diff --git a/testing/web-platform/tests/streams/transform-streams/terminate.any.js b/testing/web-platform/tests/streams/transform-streams/terminate.any.js
new file mode 100644
index 0000000000..670006366d
--- /dev/null
+++ b/testing/web-platform/tests/streams/transform-streams/terminate.any.js
@@ -0,0 +1,100 @@
+// META: global=window,worker
+// META: script=../resources/recording-streams.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+promise_test(t => {
+  const ts = recordingTransformStream({}, undefined, { highWaterMark: 0 });
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue(0);
+    }
+  });
+  let pipeToRejected = false;
+  const pipeToPromise = promise_rejects_js(t, TypeError, rs.pipeTo(ts.writable), 'pipeTo should reject').then(() => {
+    pipeToRejected = true;
+  });
+  return delay(0).then(() => {
+    assert_array_equals(ts.events, [], 'transform() should have seen no chunks');
+    assert_false(pipeToRejected, 'pipeTo() should not have rejected yet');
+    ts.controller.terminate();
+    return pipeToPromise;
+  }).then(() => {
+    assert_array_equals(ts.events, [], 'transform() should still have seen no chunks');
+    assert_true(pipeToRejected, 'pipeToRejected must be true');
+  });
+}, 'controller.terminate() should error pipeTo()');
+
+promise_test(t => {
+  const ts = recordingTransformStream({}, undefined, { highWaterMark: 1 });
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue(0);
+      controller.enqueue(1);
+    }
+  });
+  const pipeToPromise = rs.pipeTo(ts.writable);
+  return delay(0).then(() => {
+    assert_array_equals(ts.events, ['transform', 0], 'transform() should have seen one chunk');
+    ts.controller.terminate();
+    return promise_rejects_js(t, TypeError, pipeToPromise, 'pipeTo() should reject');
+  }).then(() => {
+    assert_array_equals(ts.events, ['transform', 0], 'transform() should still have seen only one chunk');
+  });
+}, 'controller.terminate() should prevent remaining chunks from being processed');
+
+test(() => {
+  new TransformStream({
+    start(controller) {
+      controller.enqueue(0);
+      controller.terminate();
+      assert_throws_js(TypeError, () => controller.enqueue(1), 'enqueue should throw');
+    }
+  });
+}, 'controller.enqueue() should throw after controller.terminate()');
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+promise_test(t => {
+  const ts = new TransformStream({
+    start(controller) {
+      controller.enqueue(0);
+      controller.terminate();
+      controller.error(error1);
+    }
+  });
+  return Promise.all([
+    promise_rejects_js(t, TypeError, ts.writable.abort(), 'abort() should reject with a TypeError'),
+    promise_rejects_exactly(t, error1, ts.readable.cancel(), 'cancel() should reject with error1'),
+    promise_rejects_exactly(t, error1, ts.readable.getReader().closed, 'closed should reject with error1')
+  ]);
+}, 'controller.error() after controller.terminate() with queued chunk should error the readable');
+
+promise_test(t => {
+  const ts = new TransformStream({
+    start(controller) {
+      controller.terminate();
+      controller.error(error1);
+    }
+  });
+  return Promise.all([
+    promise_rejects_js(t, TypeError, ts.writable.abort(), 'abort() should reject with a TypeError'),
+    ts.readable.cancel(),
+    ts.readable.getReader().closed
+  ]);
+}, 'controller.error() after controller.terminate() without queued chunk should do nothing');
+
+promise_test(() => {
+  const ts = new TransformStream({
+    flush(controller) {
+      controller.terminate();
+    }
+  });
+  const writer = ts.writable.getWriter();
+  return Promise.all([
+    writer.close(),
+    writer.closed,
+    ts.readable.getReader().closed
+  ]);
+}, 'controller.terminate() inside flush() should not prevent writer.close() from succeeding');
diff --git a/testing/web-platform/tests/streams/writable-streams/aborting.any.js b/testing/web-platform/tests/streams/writable-streams/aborting.any.js
new file mode 100644
index 0000000000..e016cd191b
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/aborting.any.js
@@ -0,0 +1,1487 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write: t.unreached_func('write() should not be called')
+  });
+
+  const writer = ws.getWriter();
+  const writePromise = writer.write('a');
+
+  const readyPromise = writer.ready;
+
+  writer.abort(error1);
+
+  assert_equals(writer.ready, readyPromise, 'the ready promise property should not change');
+
+  return Promise.all([
+    promise_rejects_exactly(t, error1, readyPromise, 'the ready promise should reject with error1'),
+    promise_rejects_exactly(t, error1, writePromise, 'the write() promise should reject with error1')
+  ]);
+}, 'Aborting a WritableStream before it starts should cause the writer\'s unsettled ready promise to reject');
+
+promise_test(t => {
+  const ws = new WritableStream();
+
+  const writer = ws.getWriter();
+  writer.write('a');
+
+  const readyPromise = writer.ready;
+
+  return readyPromise.then(() => {
+    writer.abort(error1);
+
+    assert_not_equals(writer.ready, readyPromise, 'the ready promise property should change');
+    return promise_rejects_exactly(t, error1, writer.ready, 'the ready promise should reject with error1');
+  });
+}, 'Aborting a WritableStream should cause the writer\'s fulfilled ready promise to reset to a rejected one');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+
+  writer.releaseLock();
+
+  return promise_rejects_js(t, TypeError, writer.abort(), 'abort() should reject with a TypeError');
+}, 'abort() on a released writer rejects');
+
+promise_test(t => {
+  const ws = recordingWritableStream();
+
+  return delay(0)
+    .then(() => {
+      const writer = ws.getWriter();
+
+      const abortPromise = writer.abort(error1);
+
+      return Promise.all([
+        promise_rejects_exactly(t, error1, writer.write(1), 'write(1) must reject with error1'),
+        promise_rejects_exactly(t, error1, writer.write(2), 'write(2) must reject with error1'),
+        abortPromise
+      ]);
+    })
+    .then(() => {
+      assert_array_equals(ws.events, ['abort', error1]);
+    });
+}, 'Aborting a WritableStream immediately prevents future writes');
+
+promise_test(t => {
+  const ws = recordingWritableStream();
+  const results = [];
+
+  return delay(0)
+    .then(() => {
+      const writer = ws.getWriter();
+
+      results.push(
+        writer.write(1),
+        promise_rejects_exactly(t, error1, writer.write(2), 'write(2) must reject with error1'),
+        promise_rejects_exactly(t, error1, writer.write(3), 'write(3) must reject with error1')
+      );
+
+      const abortPromise = writer.abort(error1);
+
+      results.push(
+        promise_rejects_exactly(t, error1, writer.write(4), 'write(4) must reject with error1'),
+        promise_rejects_exactly(t, error1, writer.write(5), 'write(5) must reject with error1')
+      );
+
+      return abortPromise;
+    }).then(() => {
+      assert_array_equals(ws.events, ['write', 1, 'abort', error1]);
+
+      return Promise.all(results);
+    });
+}, 'Aborting a WritableStream prevents further writes after any that are in progress');
+
+promise_test(() => {
+  const ws = new WritableStream({
+    abort() {
+      return 'Hello';
+    }
+  });
+  const writer = ws.getWriter();
+
+  return writer.abort('a').then(value => {
+    assert_equals(value, undefined, 'fulfillment value must be undefined');
+  });
+}, 'Fulfillment value of writer.abort() call must be undefined even if the underlying sink returns a non-undefined ' +
+   'value');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    abort() {
+      throw error1;
+    }
+  });
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.abort(undefined),
+    'rejection reason of abortPromise must be the error thrown by abort');
+}, 'WritableStream if sink\'s abort throws, the promise returned by writer.abort() rejects');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    abort() {
+      throw error1;
+    }
+  });
+  const writer = ws.getWriter();
+
+  const abortPromise1 = writer.abort(undefined);
+  const abortPromise2 = writer.abort(undefined);
+
+  assert_equals(abortPromise1, abortPromise2, 'the promises must be the same');
+
+  return promise_rejects_exactly(t, error1, abortPromise1, 'promise must have matching rejection');
+}, 'WritableStream if sink\'s abort throws, the promise returned by multiple writer.abort()s is the same and rejects');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    abort() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, ws.abort(undefined),
+    'rejection reason of abortPromise must be the error thrown by abort');
+}, 'WritableStream if sink\'s abort throws, the promise returned by ws.abort() rejects');
+
+promise_test(t => {
+  let resolveWritePromise;
+  const ws = new WritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    },
+    abort() {
+      throw error1;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  writer.write().catch(() => {});
+  return flushAsyncEvents().then(() => {
+    const abortPromise = writer.abort(undefined);
+
+    resolveWritePromise();
+    return promise_rejects_exactly(t, error1, abortPromise,
+      'rejection reason of abortPromise must be the error thrown by abort');
+  });
+}, 'WritableStream if sink\'s abort throws, for an abort performed during a write, the promise returned by ' +
+   'ws.abort() rejects');
+
+promise_test(() => {
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+
+  return writer.abort(error1).then(() => {
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+}, 'Aborting a WritableStream passes through the given reason');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+
+  const abortPromise = writer.abort(error1);
+
+  const events = [];
+  writer.ready.catch(() => {
+    events.push('ready');
+  });
+  writer.closed.catch(() => {
+    events.push('closed');
+  });
+
+  return Promise.all([
+    abortPromise,
+    promise_rejects_exactly(t, error1, writer.write(), 'writing should reject with error1'),
+    promise_rejects_exactly(t, error1, writer.close(), 'closing should reject with error1'),
+    promise_rejects_exactly(t, error1, writer.ready, 'ready should reject with error1'),
+    promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with error1')
+  ]).then(() => {
+    assert_array_equals(['ready', 'closed'], events, 'ready should reject before closed');
+  });
+}, 'Aborting a WritableStream puts it in an errored state with the error passed to abort()');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+
+  const writePromise = promise_rejects_exactly(t, error1, writer.write('a'),
+    'writing should reject with error1');
+
+  writer.abort(error1);
+
+  return writePromise;
+}, 'Aborting a WritableStream causes any outstanding write() promises to be rejected with the reason supplied');
+
+promise_test(t => {
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+
+  const closePromise = writer.close();
+  const abortPromise = writer.abort(error1);
+
+  return Promise.all([
+    promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with error1'),
+    promise_rejects_exactly(t, error1, closePromise, 'close() should reject with error1'),
+    abortPromise
+  ]).then(() => {
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+}, 'Closing but then immediately aborting a WritableStream causes the stream to error');
+
+promise_test(() => {
+  let resolveClose;
+  const ws = new WritableStream({
+    close() {
+      return new Promise(resolve => {
+        resolveClose = resolve;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+
+  const closePromise = writer.close();
+
+  return delay(0).then(() => {
+    const abortPromise = writer.abort(error1);
+    resolveClose();
+    return Promise.all([
+      writer.closed,
+      abortPromise,
+      closePromise
+    ]);
+  });
+}, 'Closing a WritableStream and aborting it while it closes causes the stream to ignore the abort attempt');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+
+  writer.close();
+
+  return delay(0).then(() => writer.abort());
+}, 'Aborting a WritableStream after it is closed is a no-op');
+
+promise_test(t => {
+  // Testing that per https://github.com/whatwg/streams/issues/620#issuecomment-263483953 the fallback to close was
+  // removed.
+
+  // Cannot use recordingWritableStream since it always has an abort
+  let closeCalled = false;
+  const ws = new WritableStream({
+    close() {
+      closeCalled = true;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  writer.abort(error1);
+
+  return promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with error1').then(() => {
+    assert_false(closeCalled, 'close must not have been called');
+  });
+}, 'WritableStream should NOT call underlying sink\'s close if no abort is supplied (historical)');
+
+promise_test(() => {
+  let thenCalled = false;
+  const ws = new WritableStream({
+    abort() {
+      return {
+        then(onFulfilled) {
+          thenCalled = true;
+          onFulfilled();
+        }
+      };
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.abort().then(() => assert_true(thenCalled, 'then() should be called'));
+}, 'returning a thenable from abort() should work');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      return flushAsyncEvents();
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    writer.abort(error1);
+    let closedRejected = false;
+    return Promise.all([
+      writePromise.then(() => assert_false(closedRejected, '.closed should not resolve before write()')),
+      promise_rejects_exactly(t, error1, writer.closed, '.closed should reject').then(() => {
+        closedRejected = true;
+      })
+    ]);
+  });
+}, '.closed should not resolve before fulfilled write()');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    const abortPromise = writer.abort(error2);
+    let closedRejected = false;
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise, 'write() should reject')
+          .then(() => assert_false(closedRejected, '.closed should not resolve before write()')),
+      promise_rejects_exactly(t, error2, writer.closed, '.closed should reject')
+          .then(() => {
+            closedRejected = true;
+          }),
+      abortPromise
+    ]);
+  });
+}, '.closed should not resolve before rejected write(); write() error should not overwrite abort() error');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      return flushAsyncEvents();
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 4 }));
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const settlementOrder = [];
+    return Promise.all([
+      writer.write('1').then(() => settlementOrder.push(1)),
+      promise_rejects_exactly(t, error1, writer.write('2'), 'first queued write should be rejected')
+          .then(() => settlementOrder.push(2)),
+      promise_rejects_exactly(t, error1, writer.write('3'), 'second queued write should be rejected')
+          .then(() => settlementOrder.push(3)),
+      writer.abort(error1)
+    ]).then(() => assert_array_equals([1, 2, 3], settlementOrder, 'writes should be satisfied in order'));
+  });
+}, 'writes should be satisfied in order when aborting');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 4 }));
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const settlementOrder = [];
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writer.write('1'), 'in-flight write should be rejected')
+          .then(() => settlementOrder.push(1)),
+      promise_rejects_exactly(t, error2, writer.write('2'), 'first queued write should be rejected')
+          .then(() => settlementOrder.push(2)),
+      promise_rejects_exactly(t, error2, writer.write('3'), 'second queued write should be rejected')
+          .then(() => settlementOrder.push(3)),
+      writer.abort(error2)
+    ]).then(() => assert_array_equals([1, 2, 3], settlementOrder, 'writes should be satisfied in order'));
+  });
+}, 'writes should be satisfied in order after rejected write when aborting');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writer.write('a'), 'writer.write() should reject with error from underlying write()'),
+      promise_rejects_exactly(t, error2, writer.close(),
+                              'writer.close() should reject with error from underlying write()'),
+      writer.abort(error2)
+    ]);
+  });
+}, 'close() should reject with abort reason why abort() is first error');
+
+promise_test(() => {
+  let resolveWrite;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    writer.write('a');
+    const abortPromise = writer.abort('b');
+    return flushAsyncEvents().then(() => {
+      assert_array_equals(ws.events, ['write', 'a'], 'abort should not be called while write is in-flight');
+      resolveWrite();
+      return abortPromise.then(() => {
+        assert_array_equals(ws.events, ['write', 'a', 'abort', 'b'], 'abort should be called after the write finishes');
+      });
+    });
+  });
+}, 'underlying abort() should not be called until underlying write() completes');
+
+promise_test(() => {
+  let resolveClose;
+  const ws = recordingWritableStream({
+    close() {
+      return new Promise(resolve => {
+        resolveClose = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    writer.close();
+    const abortPromise = writer.abort();
+    return flushAsyncEvents().then(() => {
+      assert_array_equals(ws.events, ['close'], 'abort should not be called while close is in-flight');
+      resolveClose();
+      return abortPromise.then(() => {
+        assert_array_equals(ws.events, ['close'], 'abort should not be called');
+      });
+    });
+  });
+}, 'underlying abort() should not be called if underlying close() has started');
+
+promise_test(t => {
+  let rejectClose;
+  let abortCalled = false;
+  const ws = new WritableStream({
+    close() {
+      return new Promise((resolve, reject) => {
+        rejectClose = reject;
+      });
+    },
+    abort() {
+      abortCalled = true;
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const closePromise = writer.close();
+    const abortPromise = writer.abort();
+    return flushAsyncEvents().then(() => {
+      assert_false(abortCalled, 'underlying abort should not be called while close is in-flight');
+      rejectClose(error1);
+      return promise_rejects_exactly(t, error1, abortPromise, 'abort should reject with the same reason').then(() => {
+        return promise_rejects_exactly(t, error1, closePromise, 'close should reject with the same reason');
+      }).then(() => {
+        assert_false(abortCalled, 'underlying abort should not be called after close completes');
+      });
+    });
+  });
+}, 'if underlying close() has started and then rejects, the abort() and close() promises should reject with the ' +
+   'underlying close rejection reason');
+
+promise_test(t => {
+  let resolveWrite;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    writer.write('a');
+    const closePromise = writer.close();
+    const abortPromise = writer.abort(error1);
+
+    return flushAsyncEvents().then(() => {
+      assert_array_equals(ws.events, ['write', 'a'], 'abort should not be called while write is in-flight');
+      resolveWrite();
+      return abortPromise.then(() => {
+        assert_array_equals(ws.events, ['write', 'a', 'abort', error1], 'abort should be called after write completes');
+        return promise_rejects_exactly(t, error1, closePromise, 'promise returned by close() should be rejected');
+      });
+    });
+  });
+}, 'an abort() that happens during a write() should trigger the underlying abort() even with a close() queued');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      return new Promise(() => {});
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    writer.write('a');
+    writer.abort(error1);
+    writer.releaseLock();
+    const writer2 = ws.getWriter();
+    return promise_rejects_exactly(t, error1, writer2.ready,
+                                   'ready of the second writer should be rejected with error1');
+  });
+}, 'if a writer is created for a stream with a pending abort, its ready should be rejected with the abort error');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const closePromise = writer.close();
+    const abortPromise = writer.abort();
+    const events = [];
+    return Promise.all([
+      closePromise.then(() => { events.push('close'); }),
+      abortPromise.then(() => { events.push('abort'); })
+    ]).then(() => {
+      assert_array_equals(events, ['close', 'abort']);
+    });
+  });
+}, 'writer close() promise should resolve before abort() promise');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write(chunk, controller) {
+      controller.error(error1);
+      return new Promise(() => {});
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    writer.write('a');
+    return promise_rejects_exactly(t, error1, writer.ready, 'writer.ready should reject');
+  });
+}, 'writer.ready should reject on controller error without waiting for underlying write');
+
+promise_test(t => {
+  let rejectWrite;
+  const ws = new WritableStream({
+    write() {
+      return new Promise((resolve, reject) => {
+        rejectWrite = reject;
+      });
+    }
+  });
+
+  let writePromise;
+  let abortPromise;
+
+  const events = [];
+
+  const writer = ws.getWriter();
+
+  writer.closed.catch(() => {
+    events.push('closed');
+  });
+
+  // Wait for ws to start
+  return flushAsyncEvents().then(() => {
+    writePromise = writer.write('a');
+    writePromise.catch(() => {
+      events.push('writePromise');
+    });
+
+    abortPromise = writer.abort(error1);
+    abortPromise.then(() => {
+      events.push('abortPromise');
+    });
+
+    const writePromise2 = writer.write('a');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise2, 'writePromise2 must reject with the error from abort'),
+      promise_rejects_exactly(t, error1, writer.ready, 'writer.ready must reject with the error from abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, [], 'writePromise, abortPromise and writer.closed must not be rejected yet');
+
+    rejectWrite(error2);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error2, writePromise,
+                              'writePromise must reject with the error returned from the sink\'s write method'),
+      abortPromise,
+      promise_rejects_exactly(t, error1, writer.closed,
+                              'writer.closed must reject with the error from abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, ['writePromise', 'abortPromise', 'closed'],
+                        'writePromise, abortPromise and writer.closed must settle');
+
+    const writePromise3 = writer.write('a');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise3,
+                              'writePromise3 must reject with the error from abort'),
+      promise_rejects_exactly(t, error1, writer.ready,
+                              'writer.ready must be still rejected with the error indicating abort')
+    ]);
+  }).then(() => {
+    writer.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.ready,
+                      'writer.ready must be rejected with an error indicating release'),
+      promise_rejects_js(t, TypeError, writer.closed,
+                      'writer.closed must be rejected with an error indicating release')
+    ]);
+  });
+}, 'writer.abort() while there is an in-flight write, and then finish the write with rejection');
+
+promise_test(t => {
+  let resolveWrite;
+  let controller;
+  const ws = new WritableStream({
+    write(chunk, c) {
+      controller = c;
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+
+  let writePromise;
+  let abortPromise;
+
+  const events = [];
+
+  const writer = ws.getWriter();
+
+  writer.closed.catch(() => {
+    events.push('closed');
+  });
+
+  // Wait for ws to start
+  return flushAsyncEvents().then(() => {
+    writePromise = writer.write('a');
+    writePromise.then(() => {
+      events.push('writePromise');
+    });
+
+    abortPromise = writer.abort(error1);
+    abortPromise.then(() => {
+      events.push('abortPromise');
+    });
+
+    const writePromise2 = writer.write('a');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise2, 'writePromise2 must reject with the error from abort'),
+      promise_rejects_exactly(t, error1, writer.ready, 'writer.ready must reject with the error from abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, [], 'writePromise, abortPromise and writer.closed must not be fulfilled/rejected yet');
+
+    // This error is too late to change anything. abort() has already changed the stream state to 'erroring'.
+    controller.error(error2);
+
+    const writePromise3 = writer.write('a');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise3,
+                              'writePromise3 must reject with the error from abort'),
+      promise_rejects_exactly(t, error1, writer.ready,
+                              'writer.ready must be still rejected with the error indicating abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(
+        events, [],
+        'writePromise, abortPromise and writer.closed must not be fulfilled/rejected yet even after ' +
+            'controller.error() call');
+
+    resolveWrite();
+
+    return Promise.all([
+      writePromise,
+      abortPromise,
+      promise_rejects_exactly(t, error1, writer.closed,
+                              'writer.closed must reject with the error from abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, ['writePromise', 'abortPromise', 'closed'],
+                        'writePromise, abortPromise and writer.closed must settle');
+
+    const writePromise4 = writer.write('a');
+
+    return Promise.all([
+      writePromise,
+      promise_rejects_exactly(t, error1, writePromise4,
+                              'writePromise4 must reject with the error from abort'),
+      promise_rejects_exactly(t, error1, writer.ready,
+                              'writer.ready must be still rejected with the error indicating abort')
+    ]);
+  }).then(() => {
+    writer.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.ready,
+                      'writer.ready must be rejected with an error indicating release'),
+      promise_rejects_js(t, TypeError, writer.closed,
+                      'writer.closed must be rejected with an error indicating release')
+    ]);
+  });
+}, 'writer.abort(), controller.error() while there is an in-flight write, and then finish the write');
+
+promise_test(t => {
+  let resolveClose;
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    },
+    close() {
+      return new Promise(resolve => {
+        resolveClose = resolve;
+      });
+    }
+  });
+
+  let closePromise;
+  let abortPromise;
+
+  const events = [];
+
+  const writer = ws.getWriter();
+
+  writer.closed.then(() => {
+    events.push('closed');
+  });
+
+  // Wait for ws to start
+  return flushAsyncEvents().then(() => {
+    closePromise = writer.close();
+    closePromise.then(() => {
+      events.push('closePromise');
+    });
+
+    abortPromise = writer.abort(error1);
+    abortPromise.then(() => {
+      events.push('abortPromise');
+    });
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.close(),
+        'writer.close() must reject with an error indicating already closing'),
+      promise_rejects_exactly(t, error1, writer.ready, 'writer.ready must reject with the error from abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, [], 'closePromise, abortPromise and writer.closed must not be fulfilled/rejected yet');
+
+    controller.error(error2);
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.close(),
+        'writer.close() must reject with an error indicating already closing'),
+      promise_rejects_exactly(t, error1, writer.ready,
+                              'writer.ready must be still rejected with the error indicating abort'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(
+        events, [],
+        'closePromise, abortPromise and writer.closed must not be fulfilled/rejected yet even after ' +
+            'controller.error() call');
+
+    resolveClose();
+
+    return Promise.all([
+      closePromise,
+      abortPromise,
+      writer.closed,
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, ['closePromise', 'abortPromise', 'closed'],
+                        'closedPromise, abortPromise and writer.closed must fulfill');
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.close(),
+        'writer.close() must reject with an error indicating already closing'),
+      promise_rejects_exactly(t, error1, writer.ready,
+                              'writer.ready must be still rejected with the error indicating abort')
+    ]);
+  }).then(() => {
+    writer.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.close(),
+        'writer.close() must reject with an error indicating release'),
+      promise_rejects_js(t, TypeError, writer.ready,
+                      'writer.ready must be rejected with an error indicating release'),
+      promise_rejects_js(t, TypeError, writer.closed,
+                      'writer.closed must be rejected with an error indicating release')
+    ]);
+  });
+}, 'writer.abort(), controller.error() while there is an in-flight close, and then finish the close');
+
+promise_test(t => {
+  let resolveWrite;
+  let controller;
+  const ws = recordingWritableStream({
+    write(chunk, c) {
+      controller = c;
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+
+  let writePromise;
+  let abortPromise;
+
+  const events = [];
+
+  const writer = ws.getWriter();
+
+  writer.closed.catch(() => {
+    events.push('closed');
+  });
+
+  // Wait for ws to start
+  return flushAsyncEvents().then(() => {
+    writePromise = writer.write('a');
+    writePromise.then(() => {
+      events.push('writePromise');
+    });
+
+    controller.error(error2);
+
+    const writePromise2 = writer.write('a');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error2, writePromise2,
+                              'writePromise2 must reject with the error passed to the controller\'s error method'),
+      promise_rejects_exactly(t, error2, writer.ready,
+                              'writer.ready must reject with the error passed to the controller\'s error method'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, [], 'writePromise and writer.closed must not be fulfilled/rejected yet');
+
+    abortPromise = writer.abort(error1);
+    abortPromise.catch(() => {
+      events.push('abortPromise');
+    });
+
+    const writePromise3 = writer.write('a');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error2, writePromise3,
+                              'writePromise3 must reject with the error passed to the controller\'s error method'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(
+        events, [],
+        'writePromise and writer.closed must not be fulfilled/rejected yet even after writer.abort()');
+
+    resolveWrite();
+
+    return Promise.all([
+      promise_rejects_exactly(t, error2, abortPromise,
+                              'abort() must reject with the error passed to the controller\'s error method'),
+      promise_rejects_exactly(t, error2, writer.closed,
+                              'writer.closed must reject with the error passed to the controller\'s error method'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, ['writePromise', 'abortPromise', 'closed'],
+                        'writePromise, abortPromise and writer.closed must fulfill/reject');
+    assert_array_equals(ws.events, ['write', 'a'], 'sink abort() should not be called');
+
+    const writePromise4 = writer.write('a');
+
+    return Promise.all([
+      writePromise,
+      promise_rejects_exactly(t, error2, writePromise4,
+                              'writePromise4 must reject with the error passed to the controller\'s error method'),
+      promise_rejects_exactly(t, error2, writer.ready,
+                              'writer.ready must be still rejected with the error passed to the controller\'s error method')
+    ]);
+  }).then(() => {
+    writer.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.ready,
+                      'writer.ready must be rejected with an error indicating release'),
+      promise_rejects_js(t, TypeError, writer.closed,
+                      'writer.closed must be rejected with an error indicating release')
+    ]);
+  });
+}, 'controller.error(), writer.abort() while there is an in-flight write, and then finish the write');
+
+promise_test(t => {
+  let resolveClose;
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    },
+    close() {
+      return new Promise(resolve => {
+        resolveClose = resolve;
+      });
+    }
+  });
+
+  let closePromise;
+  let abortPromise;
+
+  const events = [];
+
+  const writer = ws.getWriter();
+
+  writer.closed.then(() => {
+    events.push('closed');
+  });
+
+  // Wait for ws to start
+  return flushAsyncEvents().then(() => {
+    closePromise = writer.close();
+    closePromise.then(() => {
+      events.push('closePromise');
+    });
+
+    controller.error(error2);
+
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(events, [], 'closePromise must not be fulfilled/rejected yet');
+
+    abortPromise = writer.abort(error1);
+    abortPromise.then(() => {
+      events.push('abortPromise');
+    });
+
+    return Promise.all([
+      promise_rejects_exactly(t, error2, writer.ready,
+                              'writer.ready must reject with the error passed to the controller\'s error method'),
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(
+        events, [],
+        'closePromise and writer.closed must not be fulfilled/rejected yet even after writer.abort()');
+
+    resolveClose();
+
+    return Promise.all([
+      closePromise,
+      promise_rejects_exactly(t, error2, writer.ready,
+                              'writer.ready must be still rejected with the error passed to the controller\'s error method'),
+      writer.closed,
+      flushAsyncEvents()
+    ]);
+  }).then(() => {
+    assert_array_equals(events, ['closePromise', 'abortPromise', 'closed'],
+                        'abortPromise, closePromise and writer.closed must fulfill/reject');
+  }).then(() => {
+    writer.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, writer.ready,
+                      'writer.ready must be rejected with an error indicating release'),
+      promise_rejects_js(t, TypeError, writer.closed,
+                      'writer.closed must be rejected with an error indicating release')
+    ]);
+  });
+}, 'controller.error(), writer.abort() while there is an in-flight close, and then finish the close');
+
+promise_test(t => {
+  let resolveWrite;
+  const ws = new WritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    const closed = writer.closed;
+    const abortPromise = writer.abort();
+    writer.releaseLock();
+    resolveWrite();
+    return Promise.all([
+      writePromise,
+      abortPromise,
+      promise_rejects_js(t, TypeError, closed, 'closed should reject')]);
+  });
+}, 'releaseLock() while aborting should reject the original closed promise');
+
+// TODO(ricea): Consider removing this test if it is no longer useful.
+promise_test(t => {
+  let resolveWrite;
+  let resolveAbort;
+  let resolveAbortStarted;
+  const abortStarted = new Promise(resolve => {
+    resolveAbortStarted = resolve;
+  });
+  const ws = new WritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    },
+    abort() {
+      resolveAbortStarted();
+      return new Promise(resolve => {
+        resolveAbort = resolve;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    const closed = writer.closed;
+    const abortPromise = writer.abort();
+    resolveWrite();
+    return abortStarted.then(() => {
+      writer.releaseLock();
+      assert_equals(writer.closed, closed, 'closed promise should not have changed');
+      resolveAbort();
+      return Promise.all([
+        writePromise,
+        abortPromise,
+        promise_rejects_js(t, TypeError, closed, 'closed should reject')]);
+    });
+  });
+}, 'releaseLock() during delayed async abort() should reject the writer.closed promise');
+
+promise_test(() => {
+  let resolveStart;
+  const ws = recordingWritableStream({
+    start() {
+      return new Promise(resolve => {
+        resolveStart = resolve;
+      });
+    }
+  });
+  const abortPromise = ws.abort('done');
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, [], 'abort() should not be called during start()');
+    resolveStart();
+    return abortPromise.then(() => {
+      assert_array_equals(ws.events, ['abort', 'done'], 'abort() should be called after start() is done');
+    });
+  });
+}, 'sink abort() should not be called until sink start() is done');
+
+promise_test(() => {
+  let resolveStart;
+  let controller;
+  const ws = recordingWritableStream({
+    start(c) {
+      controller = c;
+      return new Promise(resolve => {
+        resolveStart = resolve;
+      });
+    }
+  });
+  const abortPromise = ws.abort('done');
+  controller.error(error1);
+  resolveStart();
+  return abortPromise.then(() =>
+      assert_array_equals(ws.events, ['abort', 'done'],
+                          'abort() should still be called if start() errors the controller'));
+}, 'if start attempts to error the controller after abort() has been called, then it should lose');
+
+promise_test(() => {
+  const ws = recordingWritableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+  return ws.abort('done').then(() =>
+      assert_array_equals(ws.events, ['abort', 'done'], 'abort() should still be called if start() rejects'));
+}, 'stream abort() promise should still resolve if sink start() rejects');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  const writerReady1 = writer.ready;
+  writer.abort(error1);
+  const writerReady2 = writer.ready;
+  assert_not_equals(writerReady1, writerReady2, 'abort() should replace the ready promise with a rejected one');
+  return Promise.all([writerReady1,
+                      promise_rejects_exactly(t, error1, writerReady2, 'writerReady2 should reject')]);
+}, 'writer abort() during sink start() should replace the writer.ready promise synchronously');
+
+promise_test(t => {
+  const events = [];
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  const writePromise1 = writer.write(1);
+  const abortPromise = writer.abort(error1);
+  const writePromise2 = writer.write(2);
+  const closePromise = writer.close();
+  writePromise1.catch(() => events.push('write1'));
+  abortPromise.then(() => events.push('abort'));
+  writePromise2.catch(() => events.push('write2'));
+  closePromise.catch(() => events.push('close'));
+  return Promise.all([
+    promise_rejects_exactly(t, error1, writePromise1, 'first write() should reject'),
+    abortPromise,
+    promise_rejects_exactly(t, error1, writePromise2, 'second write() should reject'),
+    promise_rejects_exactly(t, error1, closePromise, 'close() should reject')
+  ])
+  .then(() => {
+    assert_array_equals(events, ['write2', 'write1', 'abort', 'close'],
+                        'promises should resolve in the standard order');
+    assert_array_equals(ws.events, ['abort', error1], 'underlying sink write() should not be called');
+  });
+}, 'promises returned from other writer methods should be rejected when writer abort() happens during sink start()');
+
+promise_test(t => {
+  let writeReject;
+  let controller;
+  const ws = new WritableStream({
+    write(chunk, c) {
+      controller = c;
+      return new Promise((resolve, reject) => {
+        writeReject = reject;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    const abortPromise = writer.abort();
+    controller.error(error1);
+    writeReject(error2);
+    return Promise.all([
+      promise_rejects_exactly(t, error2, writePromise, 'write() should reject with error2'),
+      abortPromise
+    ]);
+  });
+}, 'abort() should succeed despite rejection from write');
+
+promise_test(t => {
+  let closeReject;
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    },
+    close() {
+      return new Promise((resolve, reject) => {
+        closeReject = reject;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const closePromise = writer.close();
+    const abortPromise = writer.abort();
+    controller.error(error1);
+    closeReject(error2);
+    return Promise.all([
+      promise_rejects_exactly(t, error2, closePromise, 'close() should reject with error2'),
+      promise_rejects_exactly(t, error2, abortPromise, 'abort() should reject with error2')
+    ]);
+  });
+}, 'abort() should be rejected with the rejection returned from close()');
+
+promise_test(t => {
+  let rejectWrite;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise((resolve, reject) => {
+        rejectWrite = reject;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('1');
+    const abortPromise = writer.abort(error2);
+    rejectWrite(error1);
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise, 'write should reject'),
+      abortPromise,
+      promise_rejects_exactly(t, error2, writer.closed, 'closed should reject with error2')
+    ]);
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', '1', 'abort', error2], 'abort sink method should be called');
+  });
+}, 'a rejecting sink.write() should not prevent sink.abort() from being called');
+
+promise_test(() => {
+  const ws = recordingWritableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+  return ws.abort(error2)
+      .then(() => {
+        assert_array_equals(ws.events, ['abort', error2]);
+      });
+}, 'when start errors after stream abort(), underlying sink abort() should be called anyway');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  const abortPromise1 = ws.abort();
+  const abortPromise2 = ws.abort();
+  assert_equals(abortPromise1, abortPromise2, 'the promises must be the same');
+
+  return abortPromise1.then(
+      v => assert_equals(v, undefined, 'abort() should fulfill with undefined'));
+}, 'when calling abort() twice on the same stream, both should give the same promise that fulfills with undefined');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  const abortPromise1 = ws.abort();
+
+  return abortPromise1.then(v1 => {
+    assert_equals(v1, undefined, 'first abort() should fulfill with undefined');
+
+    const abortPromise2 = ws.abort();
+    assert_not_equals(abortPromise2, abortPromise1, 'because we waited, the second promise should be a new promise');
+
+    return abortPromise2.then(v2 => {
+      assert_equals(v2, undefined, 'second abort() should fulfill with undefined');
+    });
+  });
+}, 'when calling abort() twice on the same stream, but sequentially so so there\'s no pending abort the second time, ' +
+   'both should fulfill with undefined');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.closed, 'writer.closed should reject').then(() => {
+    return writer.abort().then(
+      v => assert_equals(v, undefined, 'abort() should fulfill with undefined'));
+  });
+}, 'calling abort() on an errored stream should fulfill with undefined');
+
+promise_test(t => {
+  let controller;
+  let resolveWrite;
+  const ws = recordingWritableStream({
+    start(c) {
+      controller = c;
+    },
+    write() {
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('chunk');
+    controller.error(error1);
+    const abortPromise = writer.abort(error2);
+    resolveWrite();
+    return Promise.all([
+      writePromise,
+      promise_rejects_exactly(t, error1, abortPromise, 'abort() should reject')
+    ]).then(() => {
+      assert_array_equals(ws.events, ['write', 'chunk'], 'sink abort() should not be called');
+    });
+  });
+}, 'sink abort() should not be called if stream was erroring due to controller.error() before abort() was called');
+
+promise_test(t => {
+  let resolveWrite;
+  let size = 1;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  }, {
+    size() {
+      return size;
+    },
+    highWaterMark: 1
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise1 = writer.write('chunk1');
+    size = NaN;
+    const writePromise2 = writer.write('chunk2');
+    const abortPromise = writer.abort(error2);
+    resolveWrite();
+    return Promise.all([
+      writePromise1,
+      promise_rejects_js(t, RangeError, writePromise2, 'second write() should reject'),
+      promise_rejects_js(t, RangeError, abortPromise, 'abort() should reject')
+    ]).then(() => {
+      assert_array_equals(ws.events, ['write', 'chunk1'], 'sink abort() should not be called');
+    });
+  });
+}, 'sink abort() should not be called if stream was erroring due to bad strategy before abort() was called');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  return ws.abort().then(() => {
+    const writer = ws.getWriter();
+    return writer.closed.then(t.unreached_func('closed promise should not fulfill'),
+                              e => assert_equals(e, undefined, 'e should be undefined'));
+  });
+}, 'abort with no arguments should set the stored error to undefined');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  return ws.abort(undefined).then(() => {
+    const writer = ws.getWriter();
+    return writer.closed.then(t.unreached_func('closed promise should not fulfill'),
+                              e => assert_equals(e, undefined, 'e should be undefined'));
+  });
+}, 'abort with an undefined argument should set the stored error to undefined');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  return ws.abort('string argument').then(() => {
+    const writer = ws.getWriter();
+    return writer.closed.then(t.unreached_func('closed promise should not fulfill'),
+                              e => assert_equals(e, 'string argument', 'e should be \'string argument\''));
+  });
+}, 'abort with a string argument should set the stored error to that argument');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  return promise_rejects_js(t, TypeError, ws.abort(), 'abort should reject')
+    .then(() => writer.ready);
+}, 'abort on a locked stream should reject');
+
+test(t => {
+  let ctrl;
+  const ws = new WritableStream({start(c) { ctrl = c; }});
+  const e = Error('hello');
+
+  assert_true(ctrl.signal instanceof AbortSignal);
+  assert_false(ctrl.signal.aborted);
+  assert_equals(ctrl.signal.reason, undefined, 'signal.reason before abort');
+  ws.abort(e);
+  assert_true(ctrl.signal.aborted);
+  assert_equals(ctrl.signal.reason, e);
+}, 'WritableStreamDefaultController.signal');
+
+promise_test(async t => {
+  let ctrl;
+  let resolve;
+  const called = new Promise(r => resolve = r);
+
+  const ws = new WritableStream({
+    start(c) { ctrl = c; },
+    write() { resolve(); return new Promise(() => {}); }
+  });
+  const writer = ws.getWriter();
+
+  writer.write(99);
+  await called;
+
+  assert_false(ctrl.signal.aborted);
+  assert_equals(ctrl.signal.reason, undefined, 'signal.reason before abort');
+  writer.abort();
+  assert_true(ctrl.signal.aborted);
+  assert_true(ctrl.signal.reason instanceof DOMException, 'signal.reason is a DOMException');
+  assert_equals(ctrl.signal.reason.name, 'AbortError', 'signal.reason is an AbortError');
+}, 'the abort signal is signalled synchronously - write');
+
+promise_test(async t => {
+  let ctrl;
+  let resolve;
+  const called = new Promise(r => resolve = r);
+
+  const ws = new WritableStream({
+    start(c) { ctrl = c; },
+    close() { resolve(); return new Promise(() => {}); }
+  });
+  const writer = ws.getWriter();
+
+  writer.close(99);
+  await called;
+
+  assert_false(ctrl.signal.aborted);
+  writer.abort();
+  assert_true(ctrl.signal.aborted);
+}, 'the abort signal is signalled synchronously - close');
+
+promise_test(async t => {
+  let ctrl;
+  const ws = new WritableStream({start(c) { ctrl = c; }});
+  const writer = ws.getWriter();
+
+  const e = TypeError();
+  ctrl.error(e);
+  await promise_rejects_exactly(t, e, writer.closed);
+  assert_false(ctrl.signal.aborted);
+}, 'the abort signal is not signalled on error');
+
+promise_test(async t => {
+  let ctrl;
+  const e = TypeError();
+  const ws = new WritableStream({
+    start(c) { ctrl = c; },
+    async write() { throw e; }
+  });
+  const writer = ws.getWriter();
+
+  await promise_rejects_exactly(t, e, writer.write('hello'), 'write result');
+  await promise_rejects_exactly(t, e, writer.closed, 'closed');
+  assert_false(ctrl.signal.aborted);
+}, 'the abort signal is not signalled on write failure');
+
+promise_test(async t => {
+  let ctrl;
+  const e = TypeError();
+  const ws = new WritableStream({
+    start(c) { ctrl = c; },
+    async close() { throw e; }
+  });
+  const writer = ws.getWriter();
+
+  await promise_rejects_exactly(t, e, writer.close(), 'close result');
+  await promise_rejects_exactly(t, e, writer.closed, 'closed');
+  assert_false(ctrl.signal.aborted);
+}, 'the abort signal is not signalled on close failure');
+
+promise_test(async t => {
+  let ctrl;
+  const e1 = SyntaxError();
+  const e2 = TypeError();
+  const ws = new WritableStream({
+    start(c) { ctrl = c; },
+  });
+
+  const writer = ws.getWriter();
+  ctrl.signal.addEventListener('abort', () => writer.abort(e2));
+  writer.abort(e1);
+  assert_true(ctrl.signal.aborted);
+
+  await promise_rejects_exactly(t, e2, writer.closed, 'closed');
+}, 'recursive abort() call');
diff --git a/testing/web-platform/tests/streams/writable-streams/bad-strategies.any.js b/testing/web-platform/tests/streams/writable-streams/bad-strategies.any.js
new file mode 100644
index 0000000000..63fa443065
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/bad-strategies.any.js
@@ -0,0 +1,95 @@
+// META: global=window,worker
+'use strict';
+
+const error1 = new Error('a unique string');
+error1.name = 'error1';
+
+test(() => {
+  assert_throws_exactly(error1, () => {
+    new WritableStream({}, {
+      get size() {
+        throw error1;
+      },
+      highWaterMark: 5
+    });
+  }, 'construction should re-throw the error');
+}, 'Writable stream: throwing strategy.size getter');
+
+test(() => {
+  assert_throws_js(TypeError, () => {
+    new WritableStream({}, { size: 'a string' });
+  });
+}, 'reject any non-function value for strategy.size');
+
+test(() => {
+  assert_throws_exactly(error1, () => {
+    new WritableStream({}, {
+      size() {
+        return 1;
+      },
+      get highWaterMark() {
+        throw error1;
+      }
+    });
+  }, 'construction should re-throw the error');
+}, 'Writable stream: throwing strategy.highWaterMark getter');
+
+test(() => {
+
+  for (const highWaterMark of [-1, -Infinity, NaN, 'foo', {}]) {
+    assert_throws_js(RangeError, () => {
+      new WritableStream({}, {
+        size() {
+          return 1;
+        },
+        highWaterMark
+      });
+    }, `construction should throw a RangeError for ${highWaterMark}`);
+  }
+}, 'Writable stream: invalid strategy.highWaterMark');
+
+promise_test(t => {
+  const ws = new WritableStream({}, {
+    size() {
+      throw error1;
+    },
+    highWaterMark: 5
+  });
+
+  const writer = ws.getWriter();
+
+  const p1 = promise_rejects_exactly(t, error1, writer.write('a'), 'write should reject with the thrown error');
+
+  const p2 = promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with the thrown error');
+
+  return Promise.all([p1, p2]);
+}, 'Writable stream: throwing strategy.size method');
+
+promise_test(() => {
+  const sizes = [NaN, -Infinity, Infinity, -1];
+  return Promise.all(sizes.map(size => {
+    const ws = new WritableStream({}, {
+      size() {
+        return size;
+      },
+      highWaterMark: 5
+    });
+
+    const writer = ws.getWriter();
+
+    return writer.write('a').then(() => assert_unreached('write must reject'), writeE => {
+      assert_equals(writeE.name, 'RangeError', `write must reject with a RangeError for ${size}`);
+
+      return writer.closed.then(() => assert_unreached('write must reject'), closedE => {
+        assert_equals(closedE, writeE, `closed should reject with the same error as write`);
+      });
+    });
+  }));
+}, 'Writable stream: invalid strategy.size return value');
+
+test(() => {
+  assert_throws_js(TypeError, () => new WritableStream(undefined, {
+    size: 'not a function',
+    highWaterMark: NaN
+  }), 'WritableStream constructor should throw a TypeError');
+}, 'Writable stream: invalid size beats invalid highWaterMark');
diff --git a/testing/web-platform/tests/streams/writable-streams/bad-underlying-sinks.any.js b/testing/web-platform/tests/streams/writable-streams/bad-underlying-sinks.any.js
new file mode 100644
index 0000000000..d0b3467978
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/bad-underlying-sinks.any.js
@@ -0,0 +1,204 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+test(() => {
+  assert_throws_exactly(error1, () => {
+    new WritableStream({
+      get start() {
+        throw error1;
+      }
+    });
+  }, 'constructor should throw same error as throwing start getter');
+
+  assert_throws_exactly(error1, () => {
+    new WritableStream({
+      start() {
+        throw error1;
+      }
+    });
+  }, 'constructor should throw same error as throwing start method');
+
+  assert_throws_js(TypeError, () => {
+    new WritableStream({
+      start: 'not a function or undefined'
+    });
+  }, 'constructor should throw TypeError when passed a non-function start property');
+
+  assert_throws_js(TypeError, () => {
+    new WritableStream({
+      start: { apply() {} }
+    });
+  }, 'constructor should throw TypeError when passed a non-function start property with an .apply method');
+}, 'start: errors in start cause WritableStream constructor to throw');
+
+promise_test(t => {
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.close(), 'close() promise must reject with the thrown error')
+  .then(() => promise_rejects_exactly(t, error1, writer.ready, 'ready promise must reject with the thrown error'))
+  .then(() => promise_rejects_exactly(t, error1, writer.closed, 'closed promise must reject with the thrown error'))
+  .then(() => {
+    assert_array_equals(ws.events, ['close']);
+  });
+
+}, 'close: throwing method should cause writer close() and ready to reject');
+
+promise_test(t => {
+
+  const ws = recordingWritableStream({
+    close() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.close(), 'close() promise must reject with the same error')
+  .then(() => promise_rejects_exactly(t, error1, writer.ready, 'ready promise must reject with the same error'))
+  .then(() => assert_array_equals(ws.events, ['close']));
+
+}, 'close: returning a rejected promise should cause writer close() and ready to reject');
+
+test(() => {
+  assert_throws_exactly(error1, () => new WritableStream({
+    get close() {
+      throw error1;
+    }
+  }), 'constructor should throw');
+}, 'close: throwing getter should cause constructor to throw');
+
+test(() => {
+  assert_throws_exactly(error1, () => new WritableStream({
+    get write() {
+      throw error1;
+    }
+  }), 'constructor should throw');
+}, 'write: throwing getter should cause write() and closed to reject');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('a'), 'write should reject with the thrown error')
+  .then(() => promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with the thrown error'));
+}, 'write: throwing method should cause write() and closed to reject');
+
+promise_test(t => {
+
+  let rejectSinkWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise((r, reject) => {
+        rejectSinkWritePromise = reject;
+      });
+    }
+  });
+
+  return flushAsyncEvents().then(() => {
+    const writer = ws.getWriter();
+    const writePromise = writer.write('a');
+    rejectSinkWritePromise(error1);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writePromise, 'writer write must reject with the same error'),
+      promise_rejects_exactly(t, error1, writer.ready, 'ready promise must reject with the same error')
+    ]);
+  })
+  .then(() => {
+    assert_array_equals(ws.events, ['write', 'a']);
+  });
+
+}, 'write: returning a promise that becomes rejected after the writer write() should cause writer write() and ready ' +
+   'to reject');
+
+promise_test(t => {
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length === 2) {
+        return delay(0);
+      }
+
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  // Do not wait for this; we want to test the ready promise when the stream is "full" (desiredSize = 0), but if we wait
+  // then the stream will transition back to "empty" (desiredSize = 1)
+  writer.write('a');
+  const readyPromise = writer.ready;
+
+  return promise_rejects_exactly(t, error1, writer.write('b'), 'second write must reject with the same error').then(() => {
+    assert_equals(writer.ready, readyPromise,
+      'the ready promise must not change, since the queue was full after the first write, so the pending one simply ' +
+      'transitioned');
+    return promise_rejects_exactly(t, error1, writer.ready, 'ready promise must reject with the same error');
+  })
+  .then(() => assert_array_equals(ws.events, ['write', 'a', 'write', 'b']));
+
+}, 'write: returning a rejected promise (second write) should cause writer write() and ready to reject');
+
+test(() => {
+  assert_throws_js(TypeError, () => new WritableStream({
+    start: 'test'
+  }), 'constructor should throw');
+}, 'start: non-function start method');
+
+test(() => {
+  assert_throws_js(TypeError, () => new WritableStream({
+    write: 'test'
+  }), 'constructor should throw');
+}, 'write: non-function write method');
+
+test(() => {
+  assert_throws_js(TypeError, () => new WritableStream({
+    close: 'test'
+  }), 'constructor should throw');
+}, 'close: non-function close method');
+
+test(() => {
+  assert_throws_js(TypeError, () => new WritableStream({
+    abort: { apply() {} }
+  }), 'constructor should throw');
+}, 'abort: non-function abort method with .apply');
+
+test(() => {
+  assert_throws_exactly(error1, () => new WritableStream({
+    get abort() {
+      throw error1;
+    }
+  }), 'constructor should throw');
+}, 'abort: throwing getter should cause abort() and closed to reject');
+
+promise_test(t => {
+  const abortReason = new Error('different string');
+  const ws = new WritableStream({
+    abort() {
+      throw error1;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.abort(abortReason), 'abort should reject with the thrown error')
+  .then(() => promise_rejects_exactly(t, abortReason, writer.closed, 'closed should reject with abortReason'));
+}, 'abort: throwing method should cause abort() and closed to reject');
diff --git a/testing/web-platform/tests/streams/writable-streams/byte-length-queuing-strategy.any.js b/testing/web-platform/tests/streams/writable-streams/byte-length-queuing-strategy.any.js
new file mode 100644
index 0000000000..ce1962e891
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/byte-length-queuing-strategy.any.js
@@ -0,0 +1,28 @@
+// META: global=window,worker
+'use strict';
+
+promise_test(t => {
+  let isDone = false;
+  const ws = new WritableStream(
+    {
+      write() {
+        return new Promise(resolve => {
+          t.step_timeout(() => {
+            isDone = true;
+            resolve();
+          }, 200);
+        });
+      },
+
+      close() {
+        assert_true(isDone, 'close is only called once the promise has been resolved');
+      }
+    },
+    new ByteLengthQueuingStrategy({ highWaterMark: 1024 * 16 })
+  );
+
+  const writer = ws.getWriter();
+  writer.write({ byteLength: 1024 });
+
+  return writer.close();
+}, 'Closing a writable stream with in-flight writes below the high water mark delays the close call properly');
diff --git a/testing/web-platform/tests/streams/writable-streams/close.any.js b/testing/web-platform/tests/streams/writable-streams/close.any.js
new file mode 100644
index 0000000000..88855a92ef
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/close.any.js
@@ -0,0 +1,470 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+promise_test(() => {
+  const ws = new WritableStream({
+    close() {
+      return 'Hello';
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  const closePromise = writer.close();
+  return closePromise.then(value => assert_equals(value, undefined, 'fulfillment value must be undefined'));
+}, 'fulfillment value of writer.close() call must be undefined even if the underlying sink returns a non-undefined ' +
+    'value');
+
+promise_test(() => {
+  let controller;
+  let resolveClose;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    },
+    close() {
+      return new Promise(resolve => {
+        resolveClose = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  const closePromise = writer.close();
+  return flushAsyncEvents().then(() => {
+    controller.error(error1);
+    return flushAsyncEvents();
+  }).then(() => {
+    resolveClose();
+    return Promise.all([
+      closePromise,
+      writer.closed,
+      flushAsyncEvents().then(() => writer.closed)]);
+  });
+}, 'when sink calls error asynchronously while sink close is in-flight, the stream should not become errored');
+
+promise_test(() => {
+  let controller;
+  const passedError = new Error('error me');
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    },
+    close() {
+      controller.error(passedError);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return writer.close().then(() => writer.closed);
+}, 'when sink calls error synchronously while closing, the stream should not become errored');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return Promise.all([
+    writer.write('y'),
+    promise_rejects_exactly(t, error1, writer.close(), 'close() must reject with the error'),
+    promise_rejects_exactly(t, error1, writer.closed, 'closed must reject with the error')
+  ]);
+}, 'when the sink throws during close, and the close is requested while a write is still in-flight, the stream should ' +
+   'become errored during the close');
+
+promise_test(() => {
+  const ws = new WritableStream({
+    write(chunk, controller) {
+      controller.error(error1);
+      return new Promise(() => {});
+    }
+  });
+
+  const writer = ws.getWriter();
+  writer.write('a');
+
+  return delay(0).then(() => {
+    writer.releaseLock();
+  });
+}, 'releaseLock on a stream with a pending write in which the stream has been errored');
+
+promise_test(() => {
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    },
+    close() {
+      controller.error(error1);
+      return new Promise(() => {});
+    }
+  });
+
+  const writer = ws.getWriter();
+  writer.close();
+
+  return delay(0).then(() => {
+    writer.releaseLock();
+  });
+}, 'releaseLock on a stream with a pending close in which controller.error() was called');
+
+promise_test(() => {
+  const ws = recordingWritableStream();
+
+  const writer = ws.getWriter();
+
+  return writer.ready.then(() => {
+    assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+
+    writer.close();
+    assert_equals(writer.desiredSize, 1, 'desiredSize should be still 1');
+
+    return writer.ready.then(v => {
+      assert_equals(v, undefined, 'ready promise should be fulfilled with undefined');
+      assert_array_equals(ws.events, ['close'], 'write and abort should not be called');
+    });
+  });
+}, 'when close is called on a WritableStream in writable state, ready should return a fulfilled promise');
+
+promise_test(() => {
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(() => {});
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return writer.ready.then(() => {
+    writer.write('a');
+
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0');
+
+    let calledClose = false;
+    return Promise.all([
+      writer.ready.then(v => {
+        assert_equals(v, undefined, 'ready promise should be fulfilled with undefined');
+        assert_true(calledClose, 'ready should not be fulfilled before writer.close() is called');
+        assert_array_equals(ws.events, ['write', 'a'], 'sink abort() should not be called');
+      }),
+      flushAsyncEvents().then(() => {
+        writer.close();
+        calledClose = true;
+      })
+    ]);
+  });
+}, 'when close is called on a WritableStream in waiting state, ready promise should be fulfilled');
+
+promise_test(() => {
+  let asyncCloseFinished = false;
+  const ws = recordingWritableStream({
+    close() {
+      return flushAsyncEvents().then(() => {
+        asyncCloseFinished = true;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    writer.write('a');
+
+    writer.close();
+
+    return writer.ready.then(v => {
+      assert_false(asyncCloseFinished, 'ready promise should be fulfilled before async close completes');
+      assert_equals(v, undefined, 'ready promise should be fulfilled with undefined');
+      assert_array_equals(ws.events, ['write', 'a', 'close'], 'sink abort() should not be called');
+    });
+  });
+}, 'when close is called on a WritableStream in waiting state, ready should be fulfilled immediately even if close ' +
+    'takes a long time');
+
+promise_test(t => {
+  const rejection = { name: 'letter' };
+  const ws = new WritableStream({
+    close() {
+      return {
+        then(onFulfilled, onRejected) { onRejected(rejection); }
+      };
+    }
+  });
+  return promise_rejects_exactly(t, rejection, ws.getWriter().close(), 'close() should return a rejection');
+}, 'returning a thenable from close() should work');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const closePromise = writer.close();
+    const closedPromise = writer.closed;
+    writer.releaseLock();
+    return Promise.all([
+      closePromise,
+      promise_rejects_js(t, TypeError, closedPromise, '.closed promise should be rejected')
+    ]);
+  });
+}, 'releaseLock() should not change the result of sync close()');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    close() {
+      return flushAsyncEvents();
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const closePromise = writer.close();
+    const closedPromise = writer.closed;
+    writer.releaseLock();
+    return Promise.all([
+      closePromise,
+      promise_rejects_js(t, TypeError, closedPromise, '.closed promise should be rejected')
+    ]);
+  });
+}, 'releaseLock() should not change the result of async close()');
+
+promise_test(() => {
+  let resolveClose;
+  const ws = new WritableStream({
+    close() {
+      const promise = new Promise(resolve => {
+        resolveClose = resolve;
+      });
+      return promise;
+    }
+  });
+  const writer = ws.getWriter();
+  const closePromise = writer.close();
+  writer.releaseLock();
+  return delay(0).then(() => {
+    resolveClose();
+    return closePromise.then(() => {
+      assert_equals(ws.getWriter().desiredSize, 0, 'desiredSize should be 0');
+    });
+  });
+}, 'close() should set state to CLOSED even if writer has detached');
+
+promise_test(() => {
+  let resolveClose;
+  const ws = new WritableStream({
+    close() {
+      const promise = new Promise(resolve => {
+        resolveClose = resolve;
+      });
+      return promise;
+    }
+  });
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+  return delay(0).then(() => {
+    const abortingWriter = ws.getWriter();
+    const abortPromise = abortingWriter.abort();
+    abortingWriter.releaseLock();
+    resolveClose();
+    return abortPromise;
+  });
+}, 'the promise returned by async abort during close should resolve');
+
+// Though the order in which the promises are fulfilled or rejected is arbitrary, we're checking it for
+// interoperability. We can change the order as long as we file bugs on all implementers to update to the latest tests
+// to keep them interoperable.
+
+promise_test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+
+  const closePromise = writer.close();
+
+  const events = [];
+  return Promise.all([
+    closePromise.then(() => {
+      events.push('closePromise');
+    }),
+    writer.closed.then(() => {
+      events.push('closed');
+    })
+  ]).then(() => {
+    assert_array_equals(events, ['closePromise', 'closed'],
+                        'promises must fulfill/reject in the expected order');
+  });
+}, 'promises must fulfill/reject in the expected order on closure');
+
+promise_test(() => {
+  const ws = new WritableStream({});
+
+  // Wait until the WritableStream starts so that the close() call gets processed. Otherwise, abort() will be
+  // processed without waiting for completion of the close().
+  return delay(0).then(() => {
+    const writer = ws.getWriter();
+
+    const closePromise = writer.close();
+    const abortPromise = writer.abort(error1);
+
+    const events = [];
+    return Promise.all([
+      closePromise.then(() => {
+        events.push('closePromise');
+      }),
+      abortPromise.then(() => {
+        events.push('abortPromise');
+      }),
+      writer.closed.then(() => {
+        events.push('closed');
+      })
+    ]).then(() => {
+      assert_array_equals(events, ['closePromise', 'abortPromise', 'closed'],
+                          'promises must fulfill/reject in the expected order');
+    });
+  });
+}, 'promises must fulfill/reject in the expected order on aborted closure');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    close() {
+      return Promise.reject(error1);
+    }
+  });
+
+  // Wait until the WritableStream starts so that the close() call gets processed.
+  return delay(0).then(() => {
+    const writer = ws.getWriter();
+
+    const closePromise = writer.close();
+    const abortPromise = writer.abort(error2);
+
+    const events = [];
+    closePromise.catch(() => events.push('closePromise'));
+    abortPromise.catch(() => events.push('abortPromise'));
+    writer.closed.catch(() => events.push('closed'));
+    return Promise.all([
+      promise_rejects_exactly(t, error1, closePromise,
+                             'closePromise must reject with the error returned from the sink\'s close method'),
+      promise_rejects_exactly(t, error1, abortPromise,
+                             'abortPromise must reject with the error returned from the sink\'s close method'),
+      promise_rejects_exactly(t, error2, writer.closed,
+                              'writer.closed must reject with error2')
+    ]).then(() => {
+      assert_array_equals(events, ['closePromise', 'abortPromise', 'closed'],
+                          'promises must fulfill/reject in the expected order');
+    });
+  });
+}, 'promises must fulfill/reject in the expected order on aborted and errored closure');
+
+promise_test(t => {
+  let resolveWrite;
+  let controller;
+  const ws = new WritableStream({
+    write(chunk, c) {
+      controller = c;
+      return new Promise(resolve => {
+        resolveWrite = resolve;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    const writePromise = writer.write('c');
+    controller.error(error1);
+    const closePromise = writer.close();
+    let closeRejected = false;
+    closePromise.catch(() => {
+      closeRejected = true;
+    });
+    return flushAsyncEvents().then(() => {
+      assert_false(closeRejected);
+      resolveWrite();
+      return Promise.all([
+        writePromise,
+        promise_rejects_exactly(t, error1, closePromise, 'close() should reject')
+      ]).then(() => {
+        assert_true(closeRejected);
+      });
+    });
+  });
+}, 'close() should not reject until no sink methods are in flight');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  const writer1 = ws.getWriter();
+  return writer1.close().then(() => {
+    writer1.releaseLock();
+    const writer2 = ws.getWriter();
+    const ready = writer2.ready;
+    assert_equals(ready.constructor, Promise);
+    return ready;
+  });
+}, 'ready promise should be initialised as fulfilled for a writer on a closed stream');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  ws.close();
+  const writer = ws.getWriter();
+  return writer.closed;
+}, 'close() on a writable stream should work');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  ws.getWriter();
+  return promise_rejects_js(t, TypeError, ws.close(), 'close should reject');
+}, 'close() on a locked stream should reject');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  return promise_rejects_exactly(t, error1, ws.close(), 'close should reject with error1');
+}, 'close() on an erroring stream should reject');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  const writer = ws.getWriter();
+  return promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with the error').then(() => {
+    writer.releaseLock();
+    return promise_rejects_js(t, TypeError, ws.close(), 'close should reject');
+  });
+}, 'close() on an errored stream should reject');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  return writer.close().then(() => {
+    return promise_rejects_js(t, TypeError, ws.close(), 'close should reject');
+  });
+}, 'close() on an closed stream should reject');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    close() {
+      return new Promise(() => {});
+    }
+  });
+
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_js(t, TypeError, ws.close(), 'close should reject');
+}, 'close() on a stream with a pending close should reject');
diff --git a/testing/web-platform/tests/streams/writable-streams/constructor.any.js b/testing/web-platform/tests/streams/writable-streams/constructor.any.js
new file mode 100644
index 0000000000..eaac90e48b
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/constructor.any.js
@@ -0,0 +1,155 @@
+// META: global=window,worker
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+promise_test(() => {
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  // Now error the stream after its construction.
+  controller.error(error1);
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, null, 'desiredSize should be null');
+  return writer.closed.catch(r => {
+    assert_equals(r, error1, 'ws should be errored by the passed error');
+  });
+}, 'controller argument should be passed to start method');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write(chunk, controller) {
+      controller.error(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return Promise.all([
+    writer.write('a'),
+    promise_rejects_exactly(t, error1, writer.closed, 'controller.error() in write() should error the stream')
+  ]);
+}, 'controller argument should be passed to write method');
+
+// Older versions of the standard had the controller argument passed to close(). It wasn't useful, and so has been
+// removed. This test remains to identify implementations that haven't been updated.
+promise_test(t => {
+  const ws = new WritableStream({
+    close(...args) {
+      t.step(() => {
+        assert_array_equals(args, [], 'no arguments should be passed to close');
+      });
+    }
+  });
+
+  return ws.getWriter().close();
+}, 'controller argument should not be passed to close method');
+
+promise_test(() => {
+  const ws = new WritableStream({}, {
+    highWaterMark: 1000,
+    size() { return 1; }
+  });
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, 1000, 'desiredSize should be 1000');
+  return writer.ready.then(v => {
+    assert_equals(v, undefined, 'ready promise should fulfill with undefined');
+  });
+}, 'highWaterMark should be reflected to desiredSize');
+
+promise_test(() => {
+  const ws = new WritableStream({}, {
+    highWaterMark: Infinity,
+    size() { return 0; }
+  });
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, Infinity, 'desiredSize should be Infinity');
+
+  return writer.ready;
+}, 'WritableStream should be writable and ready should fulfill immediately if the strategy does not apply ' +
+    'backpressure');
+
+test(() => {
+  new WritableStream();
+}, 'WritableStream should be constructible with no arguments');
+
+test(() => {
+  const underlyingSink = { get start() { throw error1; } };
+  const queuingStrategy = { highWaterMark: 0, get size() { throw error2; } };
+
+  // underlyingSink is converted in prose in the method body, whereas queuingStrategy is done at the IDL layer.
+  // So the queuingStrategy exception should be encountered first.
+  assert_throws_exactly(error2, () => new WritableStream(underlyingSink, queuingStrategy));
+}, 'underlyingSink argument should be converted after queuingStrategy argument');
+
+test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+
+  assert_equals(typeof writer.write, 'function', 'writer should have a write method');
+  assert_equals(typeof writer.abort, 'function', 'writer should have an abort method');
+  assert_equals(typeof writer.close, 'function', 'writer should have a close method');
+
+  assert_equals(writer.desiredSize, 1, 'desiredSize should start at 1');
+
+  assert_not_equals(typeof writer.ready, 'undefined', 'writer should have a ready property');
+  assert_equals(typeof writer.ready.then, 'function', 'ready property should be thenable');
+  assert_not_equals(typeof writer.closed, 'undefined', 'writer should have a closed property');
+  assert_equals(typeof writer.closed.then, 'function', 'closed property should be thenable');
+}, 'WritableStream instances should have standard methods and properties');
+
+test(() => {
+  let WritableStreamDefaultController;
+  new WritableStream({
+    start(c) {
+      WritableStreamDefaultController = c.constructor;
+    }
+  });
+
+  assert_throws_js(TypeError, () => new WritableStreamDefaultController({}),
+                   'constructor should throw a TypeError exception');
+}, 'WritableStreamDefaultController constructor should throw');
+
+test(() => {
+  let WritableStreamDefaultController;
+  const stream = new WritableStream({
+    start(c) {
+      WritableStreamDefaultController = c.constructor;
+    }
+  });
+
+  assert_throws_js(TypeError, () => new WritableStreamDefaultController(stream),
+                   'constructor should throw a TypeError exception');
+}, 'WritableStreamDefaultController constructor should throw when passed an initialised WritableStream');
+
+test(() => {
+  const stream = new WritableStream();
+  const writer = stream.getWriter();
+  const WritableStreamDefaultWriter = writer.constructor;
+  writer.releaseLock();
+  assert_throws_js(TypeError, () => new WritableStreamDefaultWriter({}),
+                   'constructor should throw a TypeError exception');
+}, 'WritableStreamDefaultWriter should throw unless passed a WritableStream');
+
+test(() => {
+  const stream = new WritableStream();
+  const writer = stream.getWriter();
+  const WritableStreamDefaultWriter = writer.constructor;
+  assert_throws_js(TypeError, () => new WritableStreamDefaultWriter(stream),
+                   'constructor should throw a TypeError exception');
+}, 'WritableStreamDefaultWriter constructor should throw when stream argument is locked');
diff --git a/testing/web-platform/tests/streams/writable-streams/count-queuing-strategy.any.js b/testing/web-platform/tests/streams/writable-streams/count-queuing-strategy.any.js
new file mode 100644
index 0000000000..064e16e815
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/count-queuing-strategy.any.js
@@ -0,0 +1,124 @@
+// META: global=window,worker
+'use strict';
+
+test(() => {
+  new WritableStream({}, new CountQueuingStrategy({ highWaterMark: 4 }));
+}, 'Can construct a writable stream with a valid CountQueuingStrategy');
+
+promise_test(() => {
+  const dones = Object.create(null);
+
+  const ws = new WritableStream(
+    {
+      write(chunk) {
+        return new Promise(resolve => {
+          dones[chunk] = resolve;
+        });
+      }
+    },
+    new CountQueuingStrategy({ highWaterMark: 0 })
+  );
+
+  const writer = ws.getWriter();
+  let writePromiseB;
+  let writePromiseC;
+
+  return Promise.resolve().then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be initially 0');
+
+    const writePromiseA = writer.write('a');
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after 1st write()');
+
+    writePromiseB = writer.write('b');
+    assert_equals(writer.desiredSize, -2, 'desiredSize should be -2 after 2nd write()');
+
+    dones.a();
+    return writePromiseA;
+  }).then(() => {
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after completing 1st write()');
+
+    dones.b();
+    return writePromiseB;
+  }).then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after completing 2nd write()');
+
+    writePromiseC = writer.write('c');
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after 3rd write()');
+
+    dones.c();
+    return writePromiseC;
+  }).then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after completing 3rd write()');
+  });
+}, 'Correctly governs the value of a WritableStream\'s state property (HWM = 0)');
+
+promise_test(() => {
+  const dones = Object.create(null);
+
+  const ws = new WritableStream(
+    {
+      write(chunk) {
+        return new Promise(resolve => {
+          dones[chunk] = resolve;
+        });
+      }
+    },
+    new CountQueuingStrategy({ highWaterMark: 4 })
+  );
+
+  const writer = ws.getWriter();
+  let writePromiseB;
+  let writePromiseC;
+  let writePromiseD;
+
+  return Promise.resolve().then(() => {
+    assert_equals(writer.desiredSize, 4, 'desiredSize should be initially 4');
+
+    const writePromiseA = writer.write('a');
+    assert_equals(writer.desiredSize, 3, 'desiredSize should be 3 after 1st write()');
+
+    writePromiseB = writer.write('b');
+    assert_equals(writer.desiredSize, 2, 'desiredSize should be 2 after 2nd write()');
+
+    writePromiseC = writer.write('c');
+    assert_equals(writer.desiredSize, 1, 'desiredSize should be 1 after 3rd write()');
+
+    writePromiseD = writer.write('d');
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after 4th write()');
+
+    writer.write('e');
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after 5th write()');
+
+    writer.write('f');
+    assert_equals(writer.desiredSize, -2, 'desiredSize should be -2 after 6th write()');
+
+    writer.write('g');
+    assert_equals(writer.desiredSize, -3, 'desiredSize should be -3 after 7th write()');
+
+    dones.a();
+    return writePromiseA;
+  }).then(() => {
+    assert_equals(writer.desiredSize, -2, 'desiredSize should be -2 after completing 1st write()');
+
+    dones.b();
+    return writePromiseB;
+  }).then(() => {
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after completing 2nd write()');
+
+    dones.c();
+    return writePromiseC;
+  }).then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after completing 3rd write()');
+
+    writer.write('h');
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after 8th write()');
+
+    dones.d();
+    return writePromiseD;
+  }).then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after completing 4th write()');
+
+    writer.write('i');
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1 after 9th write()');
+  });
+}, 'Correctly governs the value of a WritableStream\'s state property (HWM = 4)');
diff --git a/testing/web-platform/tests/streams/writable-streams/error.any.js b/testing/web-platform/tests/streams/writable-streams/error.any.js
new file mode 100644
index 0000000000..faf3fdd952
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/error.any.js
@@ -0,0 +1,64 @@
+// META: global=window,worker
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+promise_test(t => {
+  const ws = new WritableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  return promise_rejects_exactly(t, error1, ws.getWriter().closed, 'stream should be errored');
+}, 'controller.error() should error the stream');
+
+test(() => {
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  ws.abort();
+  controller.error(error1);
+}, 'controller.error() on erroring stream should not throw');
+
+promise_test(t => {
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  controller.error(error1);
+  controller.error(error2);
+  return promise_rejects_exactly(t, error1, ws.getWriter().closed, 'first controller.error() should win');
+}, 'surplus calls to controller.error() should be a no-op');
+
+promise_test(() => {
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  return ws.abort().then(() => {
+    controller.error(error1);
+  });
+}, 'controller.error() on errored stream should not throw');
+
+promise_test(() => {
+  let controller;
+  const ws = new WritableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+  return ws.getWriter().close().then(() => {
+    controller.error(error1);
+  });
+}, 'controller.error() on closed stream should not throw');
diff --git a/testing/web-platform/tests/streams/writable-streams/floating-point-total-queue-size.any.js b/testing/web-platform/tests/streams/writable-streams/floating-point-total-queue-size.any.js
new file mode 100644
index 0000000000..bd34cc53a6
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/floating-point-total-queue-size.any.js
@@ -0,0 +1,87 @@
+// META: global=window,worker
+'use strict';
+
+// Due to the limitations of floating-point precision, the calculation of desiredSize sometimes gives different answers
+// than adding up the items in the queue would. It is important that implementations give the same result in these edge
+// cases so that developers do not come to depend on non-standard behaviour. See
+// https://github.com/whatwg/streams/issues/582 and linked issues for further discussion.
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(2),
+    writer.write(Number.MAX_SAFE_INTEGER)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 2 - Number.MAX_SAFE_INTEGER,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing two chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near NUMBER.MAX_SAFE_INTEGER (total ends up positive)');
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(1e-16),
+    writer.write(1)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 1e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing two chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, but clamped)');
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(1e-16),
+    writer.write(1),
+    writer.write(2e-16)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 1e-16 - 1 - 2e-16,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing three chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16 + 1 + 2e-16,
+      'desiredSize must be calculated using floating-point arithmetic (after the three chunks have finished writing)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, and not clamped)');
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(2e-16),
+    writer.write(1)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 2e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing two chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0 - 2e-16 - 1 + 2e-16 + 1,
+      'desiredSize must be calculated using floating-point arithmetic (after the two chunks have finished writing)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up zero)');
+
+function setupTestStream() {
+  const strategy = {
+    size(x) {
+      return x;
+    },
+    highWaterMark: 0
+  };
+
+  const ws = new WritableStream({}, strategy);
+
+  return ws.getWriter();
+}
diff --git a/testing/web-platform/tests/streams/writable-streams/general.any.js b/testing/web-platform/tests/streams/writable-streams/general.any.js
new file mode 100644
index 0000000000..cede7fd084
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/general.any.js
@@ -0,0 +1,277 @@
+// META: global=window,worker
+'use strict';
+
+test(() => {
+  const ws = new WritableStream({});
+  const writer = ws.getWriter();
+  writer.releaseLock();
+
+  assert_throws_js(TypeError, () => writer.desiredSize, 'desiredSize should throw a TypeError');
+}, 'desiredSize on a released writer');
+
+test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+}, 'desiredSize initial value');
+
+promise_test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+
+  writer.close();
+
+  return writer.closed.then(() => {
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0');
+  });
+}, 'desiredSize on a writer for a closed stream');
+
+test(() => {
+  const ws = new WritableStream({
+    start(c) {
+      c.error();
+    }
+  });
+
+  const writer = ws.getWriter();
+  assert_equals(writer.desiredSize, null, 'desiredSize should be null');
+}, 'desiredSize on a writer for an errored stream');
+
+test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  ws.getWriter();
+}, 'ws.getWriter() on a closing WritableStream');
+
+promise_test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+  return writer.close().then(() => {
+    writer.releaseLock();
+
+    ws.getWriter();
+  });
+}, 'ws.getWriter() on a closed WritableStream');
+
+test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+  writer.abort();
+  writer.releaseLock();
+
+  ws.getWriter();
+}, 'ws.getWriter() on an aborted WritableStream');
+
+promise_test(() => {
+  const ws = new WritableStream({
+    start(c) {
+      c.error();
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.closed.then(
+    v => assert_unreached('writer.closed fulfilled unexpectedly with: ' + v),
+    () => {
+      writer.releaseLock();
+
+      ws.getWriter();
+    }
+  );
+}, 'ws.getWriter() on an errored WritableStream');
+
+promise_test(() => {
+  const ws = new WritableStream({});
+
+  const writer = ws.getWriter();
+  writer.releaseLock();
+
+  return writer.closed.then(
+    v => assert_unreached('writer.closed fulfilled unexpectedly with: ' + v),
+    closedRejection => {
+      assert_equals(closedRejection.name, 'TypeError', 'closed promise should reject with a TypeError');
+      return writer.ready.then(
+        v => assert_unreached('writer.ready fulfilled unexpectedly with: ' + v),
+        readyRejection => assert_equals(readyRejection, closedRejection,
+          'ready promise should reject with the same error')
+      );
+    }
+  );
+}, 'closed and ready on a released writer');
+
+promise_test(t => {
+  let thisObject = null;
+  // Calls to Sink methods after the first are implicitly ignored. Only the first value that is passed to the resolver
+  // is used.
+  class Sink {
+    start() {
+      // Called twice
+      t.step(() => {
+        assert_equals(this, thisObject, 'start should be called as a method');
+      });
+    }
+
+    write() {
+      t.step(() => {
+        assert_equals(this, thisObject, 'write should be called as a method');
+      });
+    }
+
+    close() {
+      t.step(() => {
+        assert_equals(this, thisObject, 'close should be called as a method');
+      });
+    }
+
+    abort() {
+      t.step(() => {
+        assert_equals(this, thisObject, 'abort should be called as a method');
+      });
+    }
+  }
+
+  const theSink = new Sink();
+  thisObject = theSink;
+  const ws = new WritableStream(theSink);
+
+  const writer = ws.getWriter();
+
+  writer.write('a');
+  const closePromise = writer.close();
+
+  const ws2 = new WritableStream(theSink);
+  const writer2 = ws2.getWriter();
+  const abortPromise = writer2.abort();
+
+  return Promise.all([
+    closePromise,
+    abortPromise
+  ]);
+}, 'WritableStream should call underlying sink methods as methods');
+
+promise_test(t => {
+  function functionWithOverloads() {}
+  functionWithOverloads.apply = t.unreached_func('apply() should not be called');
+  functionWithOverloads.call = t.unreached_func('call() should not be called');
+  const underlyingSink = {
+    start: functionWithOverloads,
+    write: functionWithOverloads,
+    close: functionWithOverloads,
+    abort: functionWithOverloads
+  };
+  // Test start(), write(), close().
+  const ws1 = new WritableStream(underlyingSink);
+  const writer1 = ws1.getWriter();
+  writer1.write('a');
+  writer1.close();
+
+  // Test abort().
+  const abortError = new Error();
+  abortError.name = 'abort error';
+
+  const ws2 = new WritableStream(underlyingSink);
+  const writer2 = ws2.getWriter();
+  writer2.abort(abortError);
+
+  // Test abort() with a close underlying sink method present. (Historical; see
+  // https://github.com/whatwg/streams/issues/620#issuecomment-263483953 for what used to be
+  // tested here. But more coverage can't hurt.)
+  const ws3 = new WritableStream({
+    start: functionWithOverloads,
+    write: functionWithOverloads,
+    close: functionWithOverloads
+  });
+  const writer3 = ws3.getWriter();
+  writer3.abort(abortError);
+
+  return writer1.closed
+      .then(() => promise_rejects_exactly(t, abortError, writer2.closed, 'writer2.closed should be rejected'))
+      .then(() => promise_rejects_exactly(t, abortError, writer3.closed, 'writer3.closed should be rejected'));
+}, 'methods should not not have .apply() or .call() called');
+
+promise_test(() => {
+  const strategy = {
+    size() {
+      if (this !== undefined) {
+        throw new Error('size called as a method');
+      }
+      return 1;
+    }
+  };
+
+  const ws = new WritableStream({}, strategy);
+  const writer = ws.getWriter();
+  return writer.write('a');
+}, 'WritableStream\'s strategy.size should not be called as a method');
+
+promise_test(() => {
+  const ws = new WritableStream();
+  const writer1 = ws.getWriter();
+  assert_equals(undefined, writer1.releaseLock(), 'releaseLock() should return undefined');
+  const writer2 = ws.getWriter();
+  assert_equals(undefined, writer1.releaseLock(), 'no-op releaseLock() should return undefined');
+  // Calling releaseLock() on writer1 should not interfere with writer2. If it did, then the ready promise would be
+  // rejected.
+  return writer2.ready;
+}, 'redundant releaseLock() is no-op');
+
+promise_test(() => {
+  const events = [];
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    // Force the ready promise back to a pending state.
+    const writerPromise = writer.write('dummy');
+    const readyPromise = writer.ready.catch(() => events.push('ready'));
+    const closedPromise = writer.closed.catch(() => events.push('closed'));
+    writer.releaseLock();
+    return Promise.all([readyPromise, closedPromise]).then(() => {
+      assert_array_equals(events, ['ready', 'closed'], 'ready promise should fire before closed promise');
+      // Stop the writer promise hanging around after the test has finished.
+      return Promise.all([
+        writerPromise,
+        ws.abort()
+      ]);
+    });
+  });
+}, 'ready promise should fire before closed on releaseLock');
+
+test(() => {
+  class Subclass extends WritableStream {
+    extraFunction() {
+      return true;
+    }
+  }
+  assert_equals(
+      Object.getPrototypeOf(Subclass.prototype), WritableStream.prototype,
+      'Subclass.prototype\'s prototype should be WritableStream.prototype');
+  assert_equals(Object.getPrototypeOf(Subclass), WritableStream,
+                'Subclass\'s prototype should be WritableStream');
+  const sub = new Subclass();
+  assert_true(sub instanceof WritableStream,
+              'Subclass object should be an instance of WritableStream');
+  assert_true(sub instanceof Subclass,
+              'Subclass object should be an instance of Subclass');
+  const lockedGetter = Object.getOwnPropertyDescriptor(
+      WritableStream.prototype, 'locked').get;
+  assert_equals(lockedGetter.call(sub), sub.locked,
+                'Subclass object should pass brand check');
+  assert_true(sub.extraFunction(),
+              'extraFunction() should be present on Subclass object');
+}, 'Subclassing WritableStream should work');
+
+test(() => {
+  const ws = new WritableStream();
+  assert_false(ws.locked, 'stream should not be locked');
+  ws.getWriter();
+  assert_true(ws.locked, 'stream should be locked');
+}, 'the locked getter should return true if the stream has a writer');
diff --git a/testing/web-platform/tests/streams/writable-streams/properties.any.js b/testing/web-platform/tests/streams/writable-streams/properties.any.js
new file mode 100644
index 0000000000..c95bd7d0c0
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/properties.any.js
@@ -0,0 +1,53 @@
+// META: global=window,worker
+'use strict';
+
+const sinkMethods = {
+  start: {
+    length: 1,
+    trigger: () => Promise.resolve()
+  },
+  write: {
+    length: 2,
+    trigger: writer => writer.write()
+  },
+  close: {
+    length: 0,
+    trigger: writer => writer.close()
+  },
+  abort: {
+    length: 1,
+    trigger: writer => writer.abort()
+  }
+};
+
+for (const method in sinkMethods) {
+  const { length, trigger } = sinkMethods[method];
+
+  // Some semantic tests of how sink methods are called can be found in general.js, as well as in the test files
+  // specific to each method.
+  promise_test(() => {
+    let argCount;
+    const ws = new WritableStream({
+      [method](...args) {
+        argCount = args.length;
+      }
+    });
+    return Promise.resolve(trigger(ws.getWriter())).then(() => {
+      assert_equals(argCount, length, `${method} should be called with ${length} arguments`);
+    });
+  }, `sink method ${method} should be called with the right number of arguments`);
+
+  promise_test(() => {
+    let methodWasCalled = false;
+    function Sink() {}
+    Sink.prototype = {
+      [method]() {
+        methodWasCalled = true;
+      }
+    };
+    const ws = new WritableStream(new Sink());
+    return Promise.resolve(trigger(ws.getWriter())).then(() => {
+      assert_true(methodWasCalled, `${method} should be called`);
+    });
+  }, `sink method ${method} should be called even when it's located on the prototype chain`);
+}
diff --git a/testing/web-platform/tests/streams/writable-streams/reentrant-strategy.any.js b/testing/web-platform/tests/streams/writable-streams/reentrant-strategy.any.js
new file mode 100644
index 0000000000..eb05cc0680
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/reentrant-strategy.any.js
@@ -0,0 +1,174 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+// These tests exercise the pathological case of calling WritableStream* methods from within the strategy.size()
+// callback. This is not something any real code should ever do. Failures here indicate subtle deviations from the
+// standard that may affect real, non-pathological code.
+
+const error1 = { name: 'error1' };
+
+promise_test(() => {
+  let writer;
+  const strategy = {
+    size(chunk) {
+      if (chunk > 0) {
+        writer.write(chunk - 1);
+      }
+      return chunk;
+    }
+  };
+
+  const ws = recordingWritableStream({}, strategy);
+  writer = ws.getWriter();
+  return writer.write(2)
+      .then(() => {
+        assert_array_equals(ws.events, ['write', 0, 'write', 1, 'write', 2], 'writes should appear in order');
+      });
+}, 'writes should be written in the standard order');
+
+promise_test(() => {
+  let writer;
+  const events = [];
+  const strategy = {
+    size(chunk) {
+      events.push('size', chunk);
+      if (chunk > 0) {
+        writer.write(chunk - 1)
+            .then(() => events.push('writer.write done', chunk - 1));
+      }
+      return chunk;
+    }
+  };
+  const ws = new WritableStream({
+    write(chunk) {
+      events.push('sink.write', chunk);
+    }
+  }, strategy);
+  writer = ws.getWriter();
+  return writer.write(2)
+      .then(() => events.push('writer.write done', 2))
+      .then(() => flushAsyncEvents())
+      .then(() => {
+        assert_array_equals(events, ['size', 2, 'size', 1, 'size', 0,
+                                     'sink.write', 0, 'sink.write', 1, 'writer.write done', 0,
+                                     'sink.write', 2, 'writer.write done', 1,
+                                     'writer.write done', 2],
+                            'events should happen in standard order');
+      });
+}, 'writer.write() promises should resolve in the standard order');
+
+promise_test(t => {
+  let controller;
+  const strategy = {
+    size() {
+      controller.error(error1);
+      return 1;
+    }
+  };
+  const ws = recordingWritableStream({
+    start(c) {
+      controller = c;
+    }
+  }, strategy);
+  const resolved = [];
+  const writer = ws.getWriter();
+  const readyPromise1 = writer.ready.then(() => resolved.push('ready1'));
+  const writePromise = promise_rejects_exactly(t, error1, writer.write(),
+                                               'write() should reject with the error')
+                                                   .then(() => resolved.push('write'));
+  const readyPromise2 = promise_rejects_exactly(t, error1, writer.ready, 'ready should reject with error1')
+      .then(() => resolved.push('ready2'));
+  const closedPromise = promise_rejects_exactly(t, error1, writer.closed, 'closed should reject with error1')
+      .then(() => resolved.push('closed'));
+  return Promise.all([readyPromise1, writePromise, readyPromise2, closedPromise])
+      .then(() => {
+        assert_array_equals(resolved, ['ready1', 'write', 'ready2', 'closed'],
+                            'promises should resolve in standard order');
+        assert_array_equals(ws.events, [], 'underlying sink write should not be called');
+      });
+}, 'controller.error() should work when called from within strategy.size()');
+
+promise_test(t => {
+  let writer;
+  const strategy = {
+    size() {
+      writer.close();
+      return 1;
+    }
+  };
+
+  const ws = recordingWritableStream({}, strategy);
+  writer = ws.getWriter();
+  return promise_rejects_js(t, TypeError, writer.write('a'), 'write() promise should reject')
+      .then(() => {
+        assert_array_equals(ws.events, ['close'], 'sink.write() should not be called');
+      });
+}, 'close() should work when called from within strategy.size()');
+
+promise_test(t => {
+  let writer;
+  const strategy = {
+    size() {
+      writer.abort(error1);
+      return 1;
+    }
+  };
+
+  const ws = recordingWritableStream({}, strategy);
+  writer = ws.getWriter();
+  return promise_rejects_exactly(t, error1, writer.write('a'), 'write() promise should reject')
+      .then(() => {
+        assert_array_equals(ws.events, ['abort', error1], 'sink.write() should not be called');
+      });
+}, 'abort() should work when called from within strategy.size()');
+
+promise_test(t => {
+  let writer;
+  const strategy = {
+    size() {
+      writer.releaseLock();
+      return 1;
+    }
+  };
+
+  const ws = recordingWritableStream({}, strategy);
+  writer = ws.getWriter();
+  const writePromise = promise_rejects_js(t, TypeError, writer.write('a'), 'write() promise should reject');
+  const readyPromise = promise_rejects_js(t, TypeError, writer.ready, 'ready promise should reject');
+  const closedPromise = promise_rejects_js(t, TypeError, writer.closed, 'closed promise should reject');
+  return Promise.all([writePromise, readyPromise, closedPromise])
+      .then(() => {
+        assert_array_equals(ws.events, [], 'sink.write() should not be called');
+      });
+}, 'releaseLock() should abort the write() when called within strategy.size()');
+
+promise_test(t => {
+  let writer1;
+  let ws;
+  let writePromise2;
+  let closePromise;
+  let closedPromise2;
+  const strategy = {
+    size(chunk) {
+      if (chunk > 0) {
+        writer1.releaseLock();
+        const writer2 = ws.getWriter();
+        writePromise2 = writer2.write(0);
+        closePromise = writer2.close();
+        closedPromise2 = writer2.closed;
+      }
+      return 1;
+    }
+  };
+  ws = recordingWritableStream({}, strategy);
+  writer1 = ws.getWriter();
+  const writePromise1 = promise_rejects_js(t, TypeError, writer1.write(1), 'write() promise should reject');
+  const readyPromise = promise_rejects_js(t, TypeError, writer1.ready, 'ready promise should reject');
+  const closedPromise1 = promise_rejects_js(t, TypeError, writer1.closed, 'closed promise should reject');
+  return Promise.all([writePromise1, readyPromise, closedPromise1, writePromise2, closePromise, closedPromise2])
+      .then(() => {
+        assert_array_equals(ws.events, ['write', 0, 'close'], 'sink.write() should only be called once');
+      });
+}, 'original reader should error when new reader is created within strategy.size()');
diff --git a/testing/web-platform/tests/streams/writable-streams/start.any.js b/testing/web-platform/tests/streams/writable-streams/start.any.js
new file mode 100644
index 0000000000..82d869430d
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/start.any.js
@@ -0,0 +1,163 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = { name: 'error1' };
+
+promise_test(() => {
+  let resolveStartPromise;
+  const ws = recordingWritableStream({
+    start() {
+      return new Promise(resolve => {
+        resolveStartPromise = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+  writer.write('a');
+  assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after writer.write()');
+
+  // Wait and verify that write isn't called.
+  return flushAsyncEvents()
+      .then(() => {
+        assert_array_equals(ws.events, [], 'write should not be called until start promise resolves');
+        resolveStartPromise();
+        return writer.ready;
+      })
+      .then(() => assert_array_equals(ws.events, ['write', 'a'],
+                                      'write should not be called until start promise resolves'));
+}, 'underlying sink\'s write should not be called until start finishes');
+
+promise_test(() => {
+  let resolveStartPromise;
+  const ws = recordingWritableStream({
+    start() {
+      return new Promise(resolve => {
+        resolveStartPromise = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  writer.close();
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+
+  // Wait and verify that write isn't called.
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, [], 'close should not be called until start promise resolves');
+    resolveStartPromise();
+    return writer.closed;
+  });
+}, 'underlying sink\'s close should not be called until start finishes');
+
+test(() => {
+  const passedError = new Error('horrible things');
+
+  let writeCalled = false;
+  let closeCalled = false;
+  assert_throws_exactly(passedError, () => {
+    // recordingWritableStream cannot be used here because the exception in the
+    // constructor prevents assigning the object to a variable.
+    new WritableStream({
+      start() {
+        throw passedError;
+      },
+      write() {
+        writeCalled = true;
+      },
+      close() {
+        closeCalled = true;
+      }
+    });
+  }, 'constructor should throw passedError');
+  assert_false(writeCalled, 'write should not be called');
+  assert_false(closeCalled, 'close should not be called');
+}, 'underlying sink\'s write or close should not be called if start throws');
+
+promise_test(() => {
+  const ws = recordingWritableStream({
+    start() {
+      return Promise.reject();
+    }
+  });
+
+  // Wait and verify that write or close aren't called.
+  return flushAsyncEvents()
+      .then(() => assert_array_equals(ws.events, [], 'write and close should not be called'));
+}, 'underlying sink\'s write or close should not be invoked if the promise returned by start is rejected');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    start() {
+      return {
+        then(onFulfilled, onRejected) { onRejected(error1); }
+      };
+    }
+  });
+  return promise_rejects_exactly(t, error1, ws.getWriter().closed, 'closed promise should be rejected');
+}, 'returning a thenable from start() should work');
+
+promise_test(t => {
+  const ws = recordingWritableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  return promise_rejects_exactly(t, error1, ws.getWriter().write('a'), 'write() should reject with the error')
+      .then(() => {
+        assert_array_equals(ws.events, [], 'sink write() should not have been called');
+      });
+}, 'controller.error() during start should cause writes to fail');
+
+promise_test(t => {
+  let controller;
+  let resolveStart;
+  const ws = recordingWritableStream({
+    start(c) {
+      controller = c;
+      return new Promise(resolve => {
+        resolveStart = resolve;
+      });
+    }
+  });
+  const writer = ws.getWriter();
+  const writePromise = writer.write('a');
+  const closePromise = writer.close();
+  controller.error(error1);
+  resolveStart();
+  return Promise.all([
+    promise_rejects_exactly(t, error1, writePromise, 'write() should fail'),
+    promise_rejects_exactly(t, error1, closePromise, 'close() should fail')
+  ]).then(() => {
+    assert_array_equals(ws.events, [], 'sink write() and close() should not have been called');
+  });
+}, 'controller.error() during async start should cause existing writes to fail');
+
+promise_test(t => {
+  const events = [];
+  const promises = [];
+  function catchAndRecord(promise, name) {
+    promises.push(promise.then(t.unreached_func(`promise ${name} should not resolve`),
+                               () => {
+                                 events.push(name);
+                               }));
+  }
+  const ws = new WritableStream({
+    start() {
+      return Promise.reject();
+    }
+  }, { highWaterMark: 0 });
+  const writer = ws.getWriter();
+  catchAndRecord(writer.ready, 'ready');
+  catchAndRecord(writer.closed, 'closed');
+  catchAndRecord(writer.write(), 'write');
+  return Promise.all(promises)
+      .then(() => {
+        assert_array_equals(events, ['ready', 'write', 'closed'], 'promises should reject in standard order');
+      });
+}, 'when start() rejects, writer promises should reject in standard order');
diff --git a/testing/web-platform/tests/streams/writable-streams/write.any.js b/testing/web-platform/tests/streams/writable-streams/write.any.js
new file mode 100644
index 0000000000..f0246f6cad
--- /dev/null
+++ b/testing/web-platform/tests/streams/writable-streams/write.any.js
@@ -0,0 +1,284 @@
+// META: global=window,worker
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+function writeArrayToStream(array, writableStreamWriter) {
+  array.forEach(chunk => writableStreamWriter.write(chunk));
+  return writableStreamWriter.close();
+}
+
+promise_test(() => {
+  let storage;
+  const ws = new WritableStream({
+    start() {
+      storage = [];
+    },
+
+    write(chunk) {
+      return delay(0).then(() => storage.push(chunk));
+    },
+
+    close() {
+      return delay(0);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  const input = [1, 2, 3, 4, 5];
+  return writeArrayToStream(input, writer)
+      .then(() => assert_array_equals(storage, input, 'correct data should be relayed to underlying sink'));
+}, 'WritableStream should complete asynchronous writes before close resolves');
+
+promise_test(() => {
+  const ws = recordingWritableStream();
+
+  const writer = ws.getWriter();
+
+  const input = [1, 2, 3, 4, 5];
+  return writeArrayToStream(input, writer)
+      .then(() => assert_array_equals(ws.events, ['write', 1, 'write', 2, 'write', 3, 'write', 4, 'write', 5, 'close'],
+                                      'correct data should be relayed to underlying sink'));
+}, 'WritableStream should complete synchronous writes before close resolves');
+
+promise_test(() => {
+  const ws = new WritableStream({
+    write() {
+      return 'Hello';
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  const writePromise = writer.write('a');
+  return writePromise
+      .then(value => assert_equals(value, undefined, 'fulfillment value must be undefined'));
+}, 'fulfillment value of ws.write() call should be undefined even if the underlying sink returns a non-undefined ' +
+    'value');
+
+promise_test(() => {
+  let resolveSinkWritePromise;
+  const ws = new WritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveSinkWritePromise = resolve;
+      });
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    let writePromiseResolved = false;
+    assert_not_equals(resolveSinkWritePromise, undefined, 'resolveSinkWritePromise should not be undefined');
+
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0 after writer.write()');
+
+    return Promise.all([
+      writePromise.then(value => {
+        writePromiseResolved = true;
+        assert_equals(resolveSinkWritePromise, undefined, 'sinkWritePromise should be fulfilled before writePromise');
+
+        assert_equals(value, undefined, 'writePromise should be fulfilled with undefined');
+      }),
+      writer.ready.then(value => {
+        assert_equals(resolveSinkWritePromise, undefined, 'sinkWritePromise should be fulfilled before writer.ready');
+        assert_true(writePromiseResolved, 'writePromise should be fulfilled before writer.ready');
+
+        assert_equals(writer.desiredSize, 1, 'desiredSize should be 1 again');
+
+        assert_equals(value, undefined, 'writePromise should be fulfilled with undefined');
+      }),
+      flushAsyncEvents().then(() => {
+        resolveSinkWritePromise();
+        resolveSinkWritePromise = undefined;
+      })
+    ]);
+  });
+}, 'WritableStream should transition to waiting until write is acknowledged');
+
+promise_test(t => {
+  let sinkWritePromiseRejectors = [];
+  const ws = new WritableStream({
+    write() {
+      const sinkWritePromise = new Promise((r, reject) => sinkWritePromiseRejectors.push(reject));
+      return sinkWritePromise;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  assert_equals(writer.desiredSize, 1, 'desiredSize should be 1');
+
+  return writer.ready.then(() => {
+    const writePromise = writer.write('a');
+    assert_equals(sinkWritePromiseRejectors.length, 1, 'there should be 1 rejector');
+    assert_equals(writer.desiredSize, 0, 'desiredSize should be 0');
+
+    const writePromise2 = writer.write('b');
+    assert_equals(sinkWritePromiseRejectors.length, 1, 'there should be still 1 rejector');
+    assert_equals(writer.desiredSize, -1, 'desiredSize should be -1');
+
+    const closedPromise = writer.close();
+
+    assert_equals(writer.desiredSize, -1, 'desiredSize should still be -1');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, closedPromise,
+                              'closedPromise should reject with the error returned from the sink\'s write method')
+          .then(() => assert_equals(sinkWritePromiseRejectors.length, 0,
+                                    'sinkWritePromise should reject before closedPromise')),
+      promise_rejects_exactly(t, error1, writePromise,
+                              'writePromise should reject with the error returned from the sink\'s write method')
+          .then(() => assert_equals(sinkWritePromiseRejectors.length, 0,
+                                    'sinkWritePromise should reject before writePromise')),
+      promise_rejects_exactly(t, error1, writePromise2,
+                              'writePromise2 should reject with the error returned from the sink\'s write method')
+          .then(() => assert_equals(sinkWritePromiseRejectors.length, 0,
+                                    'sinkWritePromise should reject before writePromise2')),
+      flushAsyncEvents().then(() => {
+        sinkWritePromiseRejectors[0](error1);
+        sinkWritePromiseRejectors = [];
+      })
+    ]);
+  });
+}, 'when write returns a rejected promise, queued writes and close should be cleared');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('a'),
+                                 'write() should reject with the error returned from the sink\'s write method')
+      .then(() => promise_rejects_js(t, TypeError, writer.close(), 'close() should be rejected'));
+}, 'when sink\'s write throws an error, the stream should become errored and the promise should reject');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    write(chunk, controller) {
+      controller.error(error1);
+      throw error2;
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error2, writer.write('a'),
+                                 'write() should reject with the error returned from the sink\'s write method ')
+  .then(() => {
+    return Promise.all([
+      promise_rejects_exactly(t, error1, writer.ready,
+                              'writer.ready must reject with the error passed to the controller'),
+      promise_rejects_exactly(t, error1, writer.closed,
+                              'writer.closed must reject with the error passed to the controller')
+    ]);
+  });
+}, 'writer.write(), ready and closed reject with the error passed to controller.error() made before sink.write' +
+    ' rejection');
+
+promise_test(() => {
+  const numberOfWrites = 1000;
+
+  let resolveFirstWritePromise;
+  let writeCount = 0;
+  const ws = new WritableStream({
+    write() {
+      ++writeCount;
+      if (!resolveFirstWritePromise) {
+        return new Promise(resolve => {
+          resolveFirstWritePromise = resolve;
+        });
+      }
+      return Promise.resolve();
+    }
+  });
+
+  const writer = ws.getWriter();
+  return writer.ready.then(() => {
+    for (let i = 1; i < numberOfWrites; ++i) {
+      writer.write('a');
+    }
+    const writePromise = writer.write('a');
+
+    assert_equals(writeCount, 1, 'should have called sink\'s write once');
+
+    resolveFirstWritePromise();
+
+    return writePromise
+        .then(() =>
+        assert_equals(writeCount, numberOfWrites, `should have called sink's write ${numberOfWrites} times`));
+  });
+}, 'a large queue of writes should be processed completely');
+
+promise_test(() => {
+  const stream = recordingWritableStream();
+  const w = stream.getWriter();
+  const WritableStreamDefaultWriter = w.constructor;
+  w.releaseLock();
+  const writer = new WritableStreamDefaultWriter(stream);
+  return writer.ready.then(() => {
+    writer.write('a');
+    assert_array_equals(stream.events, ['write', 'a'], 'write() should be passed to sink');
+  });
+}, 'WritableStreamDefaultWriter should work when manually constructed');
+
+promise_test(() => {
+  let thenCalled = false;
+  const ws = new WritableStream({
+    write() {
+      return {
+        then(onFulfilled) {
+          thenCalled = true;
+          onFulfilled();
+        }
+      };
+    }
+  });
+  return ws.getWriter().write('a').then(() => assert_true(thenCalled, 'thenCalled should be true'));
+}, 'returning a thenable from write() should work');
+
+promise_test(() => {
+  const stream = new WritableStream();
+  const writer = stream.getWriter();
+  const WritableStreamDefaultWriter = writer.constructor;
+  assert_throws_js(TypeError, () => new WritableStreamDefaultWriter(stream),
+                   'should not be able to construct on locked stream');
+  // If stream.[[writer]] no longer points to |writer| then the closed Promise
+  // won't work properly.
+  return Promise.all([writer.close(), writer.closed]);
+}, 'failing DefaultWriter constructor should not release an existing writer');
+
+promise_test(t => {
+  const ws = new WritableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  }, { highWaterMark: 0 });
+  const writer = ws.getWriter();
+  return Promise.all([
+    promise_rejects_exactly(t, error1, writer.ready, 'ready should be rejected'),
+    promise_rejects_exactly(t, error1, writer.write(), 'write() should be rejected')
+  ]);
+}, 'write() on a stream with HWM 0 should not cause the ready Promise to resolve');
+
+promise_test(t => {
+  const ws = new WritableStream();
+  const writer = ws.getWriter();
+  writer.releaseLock();
+  return promise_rejects_js(t, TypeError, writer.write(), 'write should reject');
+}, 'writing to a released writer should reject the returned promise');