speculation-rules/prerender/resources/window-open-during-prerendering.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.

function runAsTriggerPage() {
  assert_false(document.prerendering);
  startPrerendering(location.href + '&prerendering=true');

  // Close this window for cleanup after the prerendering page runs the test.
  const bc = new PrerenderChannel('result');
  bc.onmessage = e => window.close();
}

function runAsPrerenderingPage() {
  assert_true(document.prerendering);

  // Attempt to open a window during prerendering.
  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>