chromium/third_party/blink/web_tests/custom-elements/form-validation-bubble-blur.html

<!DOCTYPE html>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<style>
control-element {
  display: inline-block;
  width: 10em;
  height: 2em;
}
</style>
<body>
<script>
class ControlElement extends HTMLElement {
  static formAssociated = true;
  constructor() {
    super();
    this.i = this.attachInternals();
    this.i.setValidity({tooShort: true}, 'Too short');
  }
}
customElements.define('control-element', ControlElement);

async_test(t => {
  assert_own_property(window, 'internals');
  document.body.insertAdjacentHTML('afterbegin', '<control-element tabindex=0></control-element>');
  let control = document.body.querySelector('control-element');
  control.i.reportValidity();
  assert_true(internals.isValidationMessageVisible(control),
              'prereq: A validation bubble should be shown.');
  assert_equals(document.activeElement, control,
                'prereq: The control should be focused.');

  control.blur();
  requestAnimationFrame(t.step_func_done(() => {
    assert_false(internals.isValidationMessageVisible(control));
  }));
}, 'Ensure that removing focus from an invalid form-associated custom ' +
    'element with a validation bubble closes the validation bubble.');
</script>
</body>