LayoutTests/webanimations/accelerated-animation-easing-and-direction-update.html

<style>

body {
    background-color: green;
}

div {
    position: absolute;
    top: 0;
    height: 100px;
}

#test {
    left: 0;
    width: 100px;
    background-color: red;
}

#reference {
    left: -1px;
    width: 102px;
    background-color: green;
}

</style>

<div id="test"></div>
<div id="reference"></div>

<script src="../resources/ui-helper.js"></script>
<script>

(async () => {
    if (window.testRunner)
        testRunner.waitUntilDone();

    const keyframes = { "transform": "translateX(600px)" };
    const easing = "cubic-bezier(1,0,1,0)";
    const duration = 10000;

    // Create two animations, a test which will change easing and direction during playback and a reference
    // which will use the test animation's changed playback throughout its entire duration. The two animations
    // should be in sync and the animated elements overlap, ensuring no red is visible after the update.
    const test = document.getElementById("test").animate(keyframes, { easing: "linear", duration });
    document.getElementById("reference").animate(keyframes, { easing, duration }).reverse();

    // Wait for the animations to be ready and to have updated once before the easing and the direction on the
    // test animation to match the reference animation.
    await Promise.all(document.getAnimations().map(animation => animation.ready));
    await UIHelper.renderingUpdate();
    test.effect.updateTiming({ easing, direction: "reverse" });

    // Wait another frame and compare the rendering.
    await UIHelper.renderingUpdate();
    if (window.testRunner)
        testRunner.notifyDone();
})();

</script>