animation-worklet/worklet-animation-play.https.html

<!DOCTYPE html>
<title>Basic use of Worklet Animation</title>
<link rel="help" href="https://drafts.css-houdini.org/css-animationworklet/">

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/web-animations/testcommon.js"></script>
<script src="common.js"></script>

<div id="target"></div>

<script>
  promise_test(async t => {
    await registerConstantLocalTimeAnimator(500);
    const effect = new KeyframeEffect(target, [{ opacity: 0 }], { duration: 1000 });
    const animation = new WorkletAnimation('constant_time', effect);
    animation.play();

    // wait until local times are synced back to the main thread.
    await waitForAnimationFrameWithCondition(_ => {
      return getComputedStyle(target).opacity != '1';
    });
    assert_equals(getComputedStyle(target).opacity, "0.5");

    animation.cancel();
  }, "A running worklet animation should output values at specified local time.");

  promise_test(async t => {
    await registerConstantLocalTimeAnimator(500);
    const effect = new KeyframeEffect(target, [{ opacity: 0 }], { duration: 1000 });
    const animation = new WorkletAnimation('constant_time', effect);
    animation.play();

    await waitForAnimationFrameWithCondition(_=> {
        return animation.playState == "running"
    });

    const prevCurrentTime = animation.currentTime;
    animation.play();
    assert_equals(animation.playState, "running");
    assert_equals(animation.currentTime, prevCurrentTime)

    animation.cancel();
  }, "Playing a running animation should be a no-op.");
</script>