Adding upstream version 124.0.1.upstream/124.0.1

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

24 files changed, 5280 insertions, 0 deletions

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..4b674bea84
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/async-iterator.any.js
@@ -0,0 +1,650 @@
+// META: global=window,worker,shadowrealm
+// 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..49fa4bdbec
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/bad-strategies.any.js
@@ -0,0 +1,198 @@
+// META: global=window,worker,shadowrealm
+'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.then(() => {
+      assert_unreached('closed didn\'t throw');
+    }, e => {
+      assert_equals(e, theError, 'closed should reject with the error for ' + size);
+    }));
+  }
+
+  return Promise.all(promises);
+
+}, 'Readable stream: invalid strategy.size return value');
+
+promise_test(() => {
+
+  const promises = [];
+  for (const size of [NaN, -Infinity, Infinity, -1]) {
+    let theError;
+    const rs = new ReadableStream(
+      {
+        pull(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.then(() => {
+      assert_unreached('closed didn\'t throw');
+    }, e => {
+      assert_equals(e, theError, 'closed should reject with the error for ' + size);
+    }));
+  }
+
+  return Promise.all(promises);
+
+}, 'Readable stream: invalid strategy.size return value when pulling');
+
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..3d77b923d1
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/bad-underlying-sources.any.js
@@ -0,0 +1,400 @@
+// META: global=window,worker,shadowrealm
+'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..9915c1fb63
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/cancel.any.js
@@ -0,0 +1,236 @@
+// META: global=window,worker,shadowrealm
+// 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..0b995f0cb1
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/constructor.any.js
@@ -0,0 +1,17 @@
+// META: global=window,worker,shadowrealm
+'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..a8c1b91d00
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/count-queuing-strategy-integration.any.js
@@ -0,0 +1,208 @@
+// META: global=window,worker,shadowrealm
+'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..f92862719e
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/default-reader.any.js
@@ -0,0 +1,539 @@
+// META: global=window,worker,shadowrealm
+// 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..8b88c21d7f
--- /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,shadowrealm
+'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/from.any.js b/testing/web-platform/tests/streams/readable-streams/from.any.js
new file mode 100644
index 0000000000..58ad4d4add
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/from.any.js
@@ -0,0 +1,474 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+'use strict';
+
+const iterableFactories = [
+  ['an array of values', () => {
+    return ['a', 'b'];
+  }],
+
+  ['an array of promises', () => {
+    return [
+      Promise.resolve('a'),
+      Promise.resolve('b')
+    ];
+  }],
+
+  ['an array iterator', () => {
+    return ['a', 'b'][Symbol.iterator]();
+  }],
+
+  ['a string', () => {
+    // This iterates over the code points of the string.
+    return 'ab';
+  }],
+
+  ['a Set', () => {
+    return new Set(['a', 'b']);
+  }],
+
+  ['a Set iterator', () => {
+    return new Set(['a', 'b'])[Symbol.iterator]();
+  }],
+
+  ['a sync generator', () => {
+    function* syncGenerator() {
+      yield 'a';
+      yield 'b';
+    }
+
+    return syncGenerator();
+  }],
+
+  ['an async generator', () => {
+    async function* asyncGenerator() {
+      yield 'a';
+      yield 'b';
+    }
+
+    return asyncGenerator();
+  }],
+
+  ['a sync iterable of values', () => {
+    const chunks = ['a', 'b'];
+    const it = {
+      next() {
+        return {
+          done: chunks.length === 0,
+          value: chunks.shift()
+        };
+      },
+      [Symbol.iterator]: () => it
+    };
+    return it;
+  }],
+
+  ['a sync iterable of promises', () => {
+    const chunks = ['a', 'b'];
+    const it = {
+      next() {
+        return chunks.length === 0 ? { done: true } : {
+          done: false,
+          value: Promise.resolve(chunks.shift())
+        };
+      },
+      [Symbol.iterator]: () => it
+    };
+    return it;
+  }],
+
+  ['an async iterable', () => {
+    const chunks = ['a', 'b'];
+    const it = {
+      next() {
+        return Promise.resolve({
+          done: chunks.length === 0,
+          value: chunks.shift()
+        })
+      },
+      [Symbol.asyncIterator]: () => it
+    };
+    return it;
+  }],
+
+  ['a ReadableStream', () => {
+    return new ReadableStream({
+      start(c) {
+        c.enqueue('a');
+        c.enqueue('b');
+        c.close();
+      }
+    });
+  }],
+
+  ['a ReadableStream async iterator', () => {
+    return new ReadableStream({
+      start(c) {
+        c.enqueue('a');
+        c.enqueue('b');
+        c.close();
+      }
+    })[Symbol.asyncIterator]();
+  }]
+];
+
+for (const [label, factory] of iterableFactories) {
+  promise_test(async () => {
+
+    const iterable = factory();
+    const rs = ReadableStream.from(iterable);
+    assert_equals(rs.constructor, ReadableStream, 'from() should return a ReadableStream');
+
+    const reader = rs.getReader();
+    assert_object_equals(await reader.read(), { value: 'a', done: false }, 'first read should be correct');
+    assert_object_equals(await reader.read(), { value: 'b', done: false }, 'second read should be correct');
+    assert_object_equals(await reader.read(), { value: undefined, done: true }, 'third read should be done');
+    await reader.closed;
+
+  }, `ReadableStream.from accepts ${label}`);
+}
+
+const badIterables = [
+  ['null', null],
+  ['undefined', undefined],
+  ['0', 0],
+  ['NaN', NaN],
+  ['true', true],
+  ['{}', {}],
+  ['Object.create(null)', Object.create(null)],
+  ['a function', () => 42],
+  ['a symbol', Symbol()],
+  ['an object with a non-callable @@iterator method', {
+    [Symbol.iterator]: 42
+  }],
+  ['an object with a non-callable @@asyncIterator method', {
+    [Symbol.asyncIterator]: 42
+  }],
+];
+
+for (const [label, iterable] of badIterables) {
+  test(() => {
+    assert_throws_js(TypeError, () => ReadableStream.from(iterable), 'from() should throw a TypeError')
+  }, `ReadableStream.from throws on invalid iterables; specifically ${label}`);
+}
+
+test(() => {
+  const theError = new Error('a unique string');
+  const iterable = {
+    [Symbol.iterator]() {
+      throw theError;
+    }
+  };
+
+  assert_throws_exactly(theError, () => ReadableStream.from(iterable), 'from() should re-throw the error');
+}, `ReadableStream.from re-throws errors from calling the @@iterator method`);
+
+test(() => {
+  const theError = new Error('a unique string');
+  const iterable = {
+    [Symbol.asyncIterator]() {
+      throw theError;
+    }
+  };
+
+  assert_throws_exactly(theError, () => ReadableStream.from(iterable), 'from() should re-throw the error');
+}, `ReadableStream.from re-throws errors from calling the @@asyncIterator method`);
+
+test(t => {
+  const theError = new Error('a unique string');
+  const iterable = {
+    [Symbol.iterator]: t.unreached_func('@@iterator should not be called'),
+    [Symbol.asyncIterator]() {
+      throw theError;
+    }
+  };
+
+  assert_throws_exactly(theError, () => ReadableStream.from(iterable), 'from() should re-throw the error');
+}, `ReadableStream.from ignores @@iterator if @@asyncIterator exists`);
+
+promise_test(async () => {
+
+  const iterable = {
+    async next() {
+      return { value: undefined, done: true };
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+
+  const read = await reader.read();
+  assert_object_equals(read, { value: undefined, done: true }, 'first read should be done');
+
+  await reader.closed;
+
+}, `ReadableStream.from accepts an empty iterable`);
+
+promise_test(async t => {
+
+  const theError = new Error('a unique string');
+
+  const iterable = {
+    async next() {
+      throw theError;
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader.read()),
+    promise_rejects_exactly(t, theError, reader.closed)
+  ]);
+
+}, `ReadableStream.from: stream errors when next() rejects`);
+
+promise_test(async t => {
+
+  const iterable = {
+    next() {
+      return new Promise(() => {});
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+
+  await Promise.race([
+    reader.read().then(t.unreached_func('read() should not resolve'), t.unreached_func('read() should not reject')),
+    reader.closed.then(t.unreached_func('closed should not resolve'), t.unreached_func('closed should not reject')),
+    flushAsyncEvents()
+  ]);
+
+}, 'ReadableStream.from: stream stalls when next() never settles');
+
+promise_test(async () => {
+
+  let nextCalls = 0;
+  let nextArgs;
+  const iterable = {
+    async next(...args) {
+      nextCalls += 1;
+      nextArgs = args;
+      return { value: 'a', done: false };
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+
+  await flushAsyncEvents();
+  assert_equals(nextCalls, 0, 'next() should not be called yet');
+
+  const read = await reader.read();
+  assert_object_equals(read, { value: 'a', done: false }, 'first read should be correct');
+  assert_equals(nextCalls, 1, 'next() should be called after first read()');
+  assert_array_equals(nextArgs, [], 'next() should be called with no arguments');
+
+}, `ReadableStream.from: calls next() after first read()`);
+
+promise_test(async t => {
+
+  const theError = new Error('a unique string');
+
+  let returnCalls = 0;
+  let returnArgs;
+  let resolveReturn;
+  const iterable = {
+    next: t.unreached_func('next() should not be called'),
+    throw: t.unreached_func('throw() should not be called'),
+    async return(...args) {
+      returnCalls += 1;
+      returnArgs = args;
+      await new Promise(r => resolveReturn = r);
+      return { done: true };
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+  assert_equals(returnCalls, 0, 'return() should not be called yet');
+
+  let cancelResolved = false;
+  const cancelPromise = reader.cancel(theError).then(() => {
+    cancelResolved = true;
+  });
+
+  await flushAsyncEvents();
+  assert_equals(returnCalls, 1, 'return() should be called');
+  assert_array_equals(returnArgs, [theError], 'return() should be called with cancel reason');
+  assert_false(cancelResolved, 'cancel() should not resolve while promise from return() is pending');
+
+  resolveReturn();
+  await Promise.all([
+    cancelPromise,
+    reader.closed
+  ]);
+
+}, `ReadableStream.from: cancelling the returned stream calls and awaits return()`);
+
+promise_test(async t => {
+
+  let nextCalls = 0;
+  let returnCalls = 0;
+
+  const iterable = {
+    async next() {
+      nextCalls += 1;
+      return { value: undefined, done: true };
+    },
+    throw: t.unreached_func('throw() should not be called'),
+    async return() {
+      returnCalls += 1;
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+
+  const read = await reader.read();
+  assert_object_equals(read, { value: undefined, done: true }, 'first read should be done');
+  assert_equals(nextCalls, 1, 'next() should be called once');
+
+  await reader.closed;
+  assert_equals(returnCalls, 0, 'return() should not be called');
+
+}, `ReadableStream.from: return() is not called when iterator completes normally`);
+
+promise_test(async t => {
+
+  const theError = new Error('a unique string');
+
+  const iterable = {
+    next: t.unreached_func('next() should not be called'),
+    throw: t.unreached_func('throw() should not be called'),
+    async return() {
+      return 42;
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  const reader = rs.getReader();
+
+  await promise_rejects_js(t, TypeError, reader.cancel(theError), 'cancel() should reject with a TypeError');
+
+  await reader.closed;
+
+}, `ReadableStream.from: cancel() rejects when return() fulfills with a non-object`);
+
+promise_test(async () => {
+
+  let nextCalls = 0;
+  let reader;
+  let values = ['a', 'b', 'c'];
+
+  const iterable = {
+    async next() {
+      nextCalls += 1;
+      if (nextCalls === 1) {
+        reader.read();
+      }
+      return { value: values.shift(), done: false };
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  reader = rs.getReader();
+
+  const read1 = await reader.read();
+  assert_object_equals(read1, { value: 'a', done: false }, 'first read should be correct');
+  await flushAsyncEvents();
+  assert_equals(nextCalls, 2, 'next() should be called two times');
+
+  const read2 = await reader.read();
+  assert_object_equals(read2, { value: 'c', done: false }, 'second read should be correct');
+  assert_equals(nextCalls, 3, 'next() should be called three times');
+
+}, `ReadableStream.from: reader.read() inside next()`);
+
+promise_test(async () => {
+
+  let nextCalls = 0;
+  let returnCalls = 0;
+  let reader;
+
+  const iterable = {
+    async next() {
+      nextCalls++;
+      await reader.cancel();
+      assert_equals(returnCalls, 1, 'return() should be called once');
+      return { value: 'something else', done: false };
+    },
+    async return() {
+      returnCalls++;
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  reader = rs.getReader();
+
+  const read = await reader.read();
+  assert_object_equals(read, { value: undefined, done: true }, 'first read should be done');
+  assert_equals(nextCalls, 1, 'next() should be called once');
+
+  await reader.closed;
+
+}, `ReadableStream.from: reader.cancel() inside next()`);
+
+promise_test(async t => {
+
+  let returnCalls = 0;
+  let reader;
+
+  const iterable = {
+    next: t.unreached_func('next() should not be called'),
+    async return() {
+      returnCalls++;
+      await reader.cancel();
+      return { done: true };
+    },
+    [Symbol.asyncIterator]: () => iterable
+  };
+
+  const rs = ReadableStream.from(iterable);
+  reader = rs.getReader();
+
+  await reader.cancel();
+  assert_equals(returnCalls, 1, 'return() should be called once');
+
+  await reader.closed;
+
+}, `ReadableStream.from: reader.cancel() inside return()`);
+
+promise_test(async t => {
+
+  let array = ['a', 'b'];
+
+  const rs = ReadableStream.from(array);
+  const reader = rs.getReader();
+
+  const read1 = await reader.read();
+  assert_object_equals(read1, { value: 'a', done: false }, 'first read should be correct');
+  const read2 = await reader.read();
+  assert_object_equals(read2, { value: 'b', done: false }, 'second read should be correct');
+
+  array.push('c');
+
+  const read3 = await reader.read();
+  assert_object_equals(read3, { value: 'c', done: false }, 'third read after push() should be correct');
+  const read4 = await reader.read();
+  assert_object_equals(read4, { value: undefined, done: true }, 'fourth read should be done');
+
+  await reader.closed;
+
+}, `ReadableStream.from(array), push() to array while reading`);
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..13bd1fb343
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/garbage-collection.any.js
@@ -0,0 +1,71 @@
+// META: global=window,worker,shadowrealm
+// 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..eee3f62215
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/general.any.js
@@ -0,0 +1,840 @@
+// META: global=window,worker,shadowrealm
+// 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..282c1f4114
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/owning-type-message-port.any.js
@@ -0,0 +1,49 @@
+// META: global=window,worker,shadowrealm
+// 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..b652f9c5fc
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/owning-type-video-frame.any.js
@@ -0,0 +1,128 @@
+// META: global=window,worker,shadowrealm
+// 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..34c2a55d51
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/owning-type.any.js
@@ -0,0 +1,91 @@
+// META: global=window,worker,shadowrealm
+// 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..c208824c86
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/patched-global.any.js
@@ -0,0 +1,142 @@
+// META: global=window,worker,shadowrealm
+'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..8ae7b98e8d
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/reentrant-strategies.any.js
@@ -0,0 +1,264 @@
+// META: global=window,worker,shadowrealm
+// 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..c2c2e48230
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/tee.any.js
@@ -0,0 +1,479 @@
+// META: global=window,worker,shadowrealm
+// 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..dc75b805a1
--- /dev/null
+++ b/testing/web-platform/tests/streams/readable-streams/templated.any.js
@@ -0,0 +1,143 @@
+// META: global=window,worker,shadowrealm
+// 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() };
+}