speculation-rules/prerender/restriction-prompt-by-before-unload.https.html

<!DOCTYPE html>
<title>Prerendering cannot invoke the prompt generated by the
       beforeunload event</title>
<meta name="timeout" content="long">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/common/utils.js"></script>
<script src="../resources/utils.js"></script>
<script src="resources/utils.js"></script>

<body>
<script>
setup(() => assertSpeculationRulesIsSupported());

promise_test(async t => {
  const uid = token();
  const bc = new PrerenderChannel('prerender-channel', uid);
  t.add_cleanup(_ => bc.close());

  const gotMessage = new Promise(resolve => {
    bc.addEventListener('message', e => {
      resolve(e.data);
    }, {
      once: true
    });
  });
  // Start prerendering a page that attempts to invoke
  // the prompt generated by the beforeunload event.
  // It is activation-gated and expects to fail.
  startPrerendering(`resources/prompt-by-before-unload.html?uid=${uid}`);

  const result = await gotMessage;
  assert_equals(result,
                'unloaded without the prompt by beforeunload.');
}, 'Prerendering cannot invoke the prompt by the beforeunload event.');
</script>