<!DOCTYPE html>
<script src="../../spec/resources/custom-elements-helpers.js"></script>
<div id="sandbox"></div>
<script>
'use strict';

test(() => {
  let constructors = [];
  assert_equals(constructors.length, 0);

  class MyElement extends HTMLElement {
    constructor() {
      super();
      constructors.push(this);
    }
  }
  customElements.define('a-a', MyElement);

  let importDoc = document.currentScript.ownerDocument;
  let sandbox = importDoc.querySelector('#sandbox');

  sandbox.innerHTML = '<a