mozilla-release/testing/web-platform/tests/clipboard-apis/detached-iframe/clipboard-on-detached-iframe.https.html

<!doctype html>
<meta charset=utf-8>
<title>Clipboard API on detached iframe</title>
<link rel='help' href='https://w3c.github.io/clipboard-apis/#async-clipboard-api'>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<iframe id="iframe"></iframe>
<script>
'use strict';

promise_test(async () => {
  const iframe = document.getElementById('iframe');
  const iframeNavigator = iframe.contentWindow.navigator;
  assert_not_equals(navigator.clipboard, null,
      "parent frame's clipboard should exist with iframe attached");
  assert_not_equals(iframeNavigator.clipboard, null,
      "attached child iframe's clipboard should exist");

  iframe.parentNode.removeChild(iframe);
  assert_not_equals(navigator.clipboard, null,
      "parent frame's clipboard should exist with iframe detached");
  assert_equals(iframeNavigator.clipboard, null,
      "detached child iframe's clipboard should not exist");
}, 'Verify navigator.clipboard attached only on attached frames');
</script>