chromium/third_party/blink/web_tests/editing/text-iterator/beforematch-bubbles.html

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

<div id=parentid>
  <div id=childid hidden=until-found>hello</div>
</div>

<script>
async_test(t => {
  parentid.addEventListener('beforematch', t.step_func_done(() => {}));
  testRunner.findString('hello', []);
}, `Tests that the beforematch event bubbles when using find-in-page.`);
</script>