speculation-rules/prerender/resources/window-open-in-prerenderingchange.html

<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="utils.js"></script>
<script>

// This file is loaded twice. First this is loaded as a page to trigger
// prerendering and then loaded as a prerendering page. The trigger page
// activates the prerendering page.

// Runs as the trigger page. This page starts prerendering and waits for signal
// from the prerendering page. After the signal, this page starts activation.
function runAsTriggerPage() {
  assert_false(document.prerendering);

  // Start prerendering.
  const prerendering_url = location.href + '&prerendering=true';
  startPrerendering(prerendering_url);

  // Activate the prerendering page once it gets ready.
  const bc = new PrerenderChannel('activation-ready');
  bc.onmessage = () => { window.location = prerendering_url };
}

// Runs as prerendeirng page. First this page waits for the load event and
// signals to the trigger page for starting activation. Then, this page fires
// the prerenderingchange event and tests window.open() in the event.
function runAsPrerenderingPage() {
  assert_true(document.prerendering);

  window.onload = () => {
    assert_true(document.prerendering);

    // Notify the trigger page of activation ready.
    const bc = new PrerenderChannel('activation-ready');
    bc.postMessage('ready for activation');
  }

  new PrerenderChannel('close').addEventListener('message', () => {
    window.close();
  });
  document.onprerenderingchange = () => {
    assert_false(document.prerendering);

    // Attempt to open a window in the prerenderingchange event.
    const win = window.open('empty.html', '_blank');

    // Send the result to the test runner page.
    const bc = new PrerenderChannel('result');
    if (win) {
      bc.postMessage('opened');
      win.close();
    } else {
      bc.postMessage('failed to open');
    }
  };
}

if (new URLSearchParams(location.search).has('prerendering')) {
  runAsPrerenderingPage();
} else {
  runAsTriggerPage();
}

</script>