<pre id="results"></pre>
<div id="target" style="width: 100px; height: 100px; background-color: black;"></div>
<script>

const animation = document.getElementById("target").animate([
    { opacity: 1 },
    { opacity: 0 }
], 100);

testRunner.waitUntilDone();
testRunner.dumpAsText();

setTimeout(() => {
    document.getElementById("results").innerText = internals.layerTreeAsText(document);
    testRunner.notifyDone();
}, animation.effect.getTiming().duration + 500);

</script>