form-validation-bubble-appearance.html

<!DOCTYPE html>
<body>
<p>Check if a validation bubble is shown</p>
<script>
class MyControl extends HTMLElement {
  static get formAssociated() { return true; }

  constructor() {
    super();
    this.internals_ = this.attachInternals();
  }
  get i() { return this.internals_; }
}

customElements.define('my-control', MyControl);
</script>
<my-control title="Please specify four digits." tabindex=0>&#x1f196;</my-control>
<script>
const myControl = document.querySelector('my-control');
myControl.i.setValidity({patternMismatch:true}, 'The value does not match to the requested format');
myControl.i.reportValidity();
</script>
<body>

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