chromium/third_party/blink/web_tests/fast/dom/shadow/dynamically-created-shadow-root.html

<!DOCTYPE html>
<body>
<div>
This tests that dynamically created ShadowRoot should be rendered correctly.
Can only run within DRT.
</div>
<div id="host1">Light children should not be rendered.</div>
<script>
if (window.internals) {
    var host1 = document.querySelector('#host1');
    var shadowRoot = host1.attachShadow({mode: 'open'});
    shadowRoot.appendChild(document.createTextNode('Shadow should be rendered.'));
}
</script>
</body>
</html>