css/css-animations/animationevent-pseudoelement.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Animations Test: AnimationEvent pseudoElement</title>
<link rel="help" href="https://drafts.csswg.org/css-animations/#interface-animationevent">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  #target::before {
    content: "";
    animation: move 1s;
  }

  @keyframes move {
    to { transform: translate(100px); }
  }
</style>
<div id='target'></div>
<script>
  async_test(function(t) {
    var target = document.getElementById('target');
    target.addEventListener("animationstart", t.step_func(function(evt) {
      assert_true(evt instanceof window.AnimationEvent);
      assert_equals(evt.pseudoElement, "::before");

      t.done();
    }), true);
  }, "AnimationEvent should have the correct pseudoElement memeber");
</script>