LayoutTests/legacy-animation-engine/animations/large-negative-delay.html

<style>
#box {
    position: relative;
    height: 100px;
    width: 100px;
    background-color: blue;
    animation-name: move;
    animation-duration: 0.2s;
    animation-iteration-count: infinite;
    animation-timing-function: linear;
    animation-delay: -999999s;
}

@keyframes move {
      0% { left: 0; }
    100% { left: 300px; }
}
</style>
<script>
if (window.testRunner) {
    testRunner.waitUntilDone();
    testRunner.dumpAsText();
}

function output(msg) {
    document.getElementById('result').innerHTML += `${msg}<br>`;
}

function iterated(event) {
    output("PASS: Saw iteration event. The animation did start.");

    if (event.elapsedTime > 1000)
        output("PASS: Elapsed time is large. The animation thinks it started a long time ago.");
    else
        output("FAIL: Elapsed time wasn't big enough.");

    if (window.testRunner)
        testRunner.notifyDone();
}

window.addEventListener("animationiteration", iterated, { once: true });
</script>
<div id="box"></div>
<div id="result"></div>