chromium/third_party/blink/web_tests/fast/forms/validation-bubble-update.html

<!DOCTYPE html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<select required></select>
<script>
var t = async_test('Ensure that adding an OPTION to a SELECT element closes a validation bubble.');
var select = document.querySelector('select');
t.step(() => {
  assert_own_property(window, 'internals');
  select.reportValidity();
  assert_true(internals.isValidationMessageVisible(select));
  select.appendChild(new Option('value'));
  t.step_timeout(() => {
    assert_false(internals.isValidationMessageVisible(select));
    t.done();
  }, 100);
});
</script>