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

const animation = new Animation(new KeyframeEffect(document.getElementById("target"), [
    { left: 0, opacity: 1 },
    { left: "100px", opacity: 0 }
]));
animation.startTime = 0;
animation.effect.updateTiming({ duration : 1000 });

testRunner.dumpAsText();
document.getElementById("results").innerText = internals.layerTreeAsText(document);

</script>