1 files changed, 25 insertions, 0 deletions
diff --git a/testing/web-platform/tests/websockets/stream/tentative/backpressure-send.any.js b/testing/web-platform/tests/websockets/stream/tentative/backpressure-send.any.js
new file mode 100644
index 0000000000..e4a80f6e1c
--- /dev/null
+++ b/testing/web-platform/tests/websockets/stream/tentative/backpressure-send.any.js
@@ -0,0 +1,25 @@
+// META: script=../../constants.sub.js
+// META: script=resources/url-constants.js
+// META: global=window,worker
+// META: timeout=long
+// META: variant=?wss
+// META: variant=?wpt_flags=h2
+
+// Allow for this much timer jitter.
+const JITTER_ALLOWANCE_MS = 200;
+
+// The amount of buffering a WebSocket connection has is not standardised, but
+// it's reasonable to expect that it will not be as large as 8MB.
+const MESSAGE_SIZE = 8 * 1024 * 1024;
+
+// In this test, the server WebSocket handler waits 2 seconds, and the browser
+// times how long it takes to send the first message.
+promise_test(async t => {
+  const wss = new WebSocketStream(`${BASEURL}/receive-backpressure`);
+  const { writable } = await wss.opened;
+  const writer = writable.getWriter();
+  const start = performance.now();
+  await writer.write(new Uint8Array(MESSAGE_SIZE));
+  const elapsed = performance.now() - start;
+  assert_greater_than_equal(elapsed, 2000 - JITTER_ALLOWANCE_MS);
+}, 'backpressure should be applied to sent messages');