1 files changed, 46 insertions, 0 deletions
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");