mozilla-release/testing/web-platform/tests/html/cross-origin-opener-policy/popup-same-origin-non-initial-about-blank.https.html

<!doctype html>
<title>Cross-Origin-Opener-Policy: about:blank</title>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<script>
async_test(t => {
  const popup = window.open("resources/coop-coep.py?coop=same-origin&coep=&navigate=about:blank");
  assert_equals(window, popup.opener);
  window.onload = t.step_func(() => {
    t.step_timeout(() => {
      assert_equals(popup.location.href, "about:blank");
      popup.close();
      t.done();
    }, 1500);
  });
}, "Navigating a popup to about:blank");
</script>