LayoutTests/webanimations/combining-transform-animations-with-different-acceleration-capabilities-3.html

<div id="target" style="width: 100px; height: 100px; background-color: black;"></div>
<script src="../resources/js-test.js"></script>
<script>

const element = document.getElementById("target");
const duration = 1000;
const iterations = Infinity;

const shouldBecomeEqualAsync = async (actual, expected) => new Promise(resolve => shouldBecomeEqual(actual, expected, resolve));

(async () => {
    if (!window.testRunner || !window.internals) {
        debug("This test should be run in a test runner.");
        return;
    }

    testRunner.waitUntilDone();

    // First, start a transform-related animation that can be accelerated.
    element.animate({ scale: [1, 2] }, { duration, iterations });
    await shouldBecomeEqualAsync("internals.acceleratedAnimationsForElement(element).length", "1");

    // Now, start another transform-related animation that cannot be accelerated due to using
    // steps() easing. This should not only prevent this animation from running accelerated,
    // but also make the previous animation revert to a non-accelerated state.
    element.animate({ rotate: ["30deg", "60deg"] }, { duration, iterations, easing: "steps(60)" });
    await shouldBecomeEqualAsync("internals.acceleratedAnimationsForElement(element).length", "0");

    testRunner.notifyDone();
})();
    
</script>