pagereveal-no-view-transition-new-opt-out.html

<!DOCTYPE html>
<title>
  View transitions: null event.viewTransition when new page removes opt-in
  before pagereveal
</title>
<link rel="help" href="https://drafts.csswg.org/css-view-transitions-2/">
<link rel="author" href="mailto:[email protected]">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style id="vt-style">
  @view-transition {
    navigation: auto;
  }
</style>
<script>
const params = new URLSearchParams(location.search.substr(1));
const is_starting_page = !params.has('new');

if (is_starting_page) {
  requestAnimationFrame(() => requestAnimationFrame( () => {
    location.replace(location.href + '?new');
  }));
} else {
  // Remove the opt-in from the destination page.
  document.querySelector("#vt-style").remove();
  promise_test(async () => {
    const pagereveal = await new Promise(resolve => {
      addEventListener('pagereveal', e => resolve(e));
    });
    assert_true('viewTransition' in pagereveal,
        '`pagereveal` must have a `viewTransition` property.');
    assert_equals(pagereveal.viewTransition, null,
        '`viewTransition` must be null when there is no opt-in.');
  });
}
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-view-transitions/navigation/pagereveal-no-view-transition-new-opt-out.html