chromium/third_party/blink/web_tests/custom-elements/spec/remove-element.html

<!DOCTYPE html>
<title>Custom Elements: Remove an element</title>
<link rel="help" href="https://dom.spec.whatwg.org/#concept-node-remove">
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="resources/custom-elements-helpers.js"></script>
<body>
<script>
'use strict';

// 15. For each shadow-including descendant descendant of node, in shadow-including tree order,
// run these substeps:
//   2. If descendant is custom, then enqueue a custom element callback reaction with descendant,
//      callback name "disconnectedCallback", and an empty argument list.
test_with_window((w) => {
  w.document.body.innerHTML = `
<a-a id="a">
  <p>
    <a-a id="b"></a-a>
    <a-a id="c"></a-a>
  </p>
  <a-a id="d"></a-a>
</a-a>`;
  let invocations = [];
  class X extends w.HTMLElement {
    disconnectedCallback() { invocations.push(this); }
  }
  w.customElements.define('a-a', X);
  w.document.getElementById("a").remove();
  assert_array_equals(['a', 'b', 'c', 'd'], invocations.map((e) => e.id),
                      'four elements should have been removed in doc order');
},'Remove an element');
</script>
</body>