chromium/third_party/blink/web_tests/animations/prefixed/animation-events-prefixed-02.html

<!DOCTYPE html>
<title>Tests that unprefixed animation events are correctly fired when listeners are on both versions.</title>
<style>
#box {
  position: relative;
  left: 100px;
  top: 10px;
  height: 100px;
  width: 100px;
  background-color: #999;
}

.animate {
  animation-duration: 0.3s;
  animation-name: anim;
}

@keyframes anim {
    from { left: 200px; }
    to   { left: 300px; }
}
</style>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script>
var startEventReceived = false;
var endEventReceived = false;
var prefixedEventReceived = 0;

document.addEventListener('webkitAnimationStart', () => {
  prefixedEventReceived++;
});

document.addEventListener('animationstart', () => {
  startEventReceived = true;
});

document.addEventListener('webkitAnimationIteration', () => {
  prefixedEventReceived++;
});

document.addEventListener('webkitAnimationEnd', () => {
  prefixedEventReceived++;
});

document.addEventListener('animationend', () => {
  endEventReceived = true;
  document.getElementById('box').className = '';

  document.getElementById('box').offsetTop; // force style recalc

  // Launch again the animation to catch the animation iteration events this time.
  document.getElementById('box').style.animationIterationCount = "infinite";
  document.getElementById('box').className = 'animate';
});

async_test(t => {
  window.addEventListener("load", t.step_func(() => {
    // Animation begins once we append the DOM node to the document.
    var boxNode = document.createElement('div');
    boxNode.id = 'box';
    boxNode.className = 'animate';
    document.body.appendChild(boxNode);
    document.addEventListener('animationiteration', t.step_func_done(() => {
      assert_true(startEventReceived);
      assert_true(endEventReceived);
      assert_equals(prefixedEventReceived, 0);
    }));
  }));
}, "Tests that unprefixed animation events are correctly fired when listeners are on both versions");
</script>