1 files changed, 19 insertions, 0 deletions
diff --git a/testing/web-platform/tests/webmessaging/message-channels/003.html b/testing/web-platform/tests/webmessaging/message-channels/003.html
new file mode 100644
index 000000000..7addaeb0f
--- /dev/null
+++ b/testing/web-platform/tests/webmessaging/message-channels/003.html
@@ -0,0 +1,19 @@
+<!doctype html>
+<title>onmessage implied start()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+async_test(function(t) {
+  var channel = new MessageChannel();
+  channel.port1.postMessage(1);
+  channel.port2.onmessage = function() {
+    setTimeout(t.step_func(function() {
+      t.done();
+    }), 50);
+    channel.port2.onmessage = t.step_func(function() {
+      assert_unreached();
+    });
+  }; // implies start()
+});
+</script>