<!DOCTYPE html>
<link rel="author" title="Tim Nguyen" href="https://github.com/nt1m">
<link rel="help" href="https://drafts.csswg.org/css-display-4/#display-animation">
<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/6429">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/css/css-animations/support/testcommon.js"></script>

<div id="target">hello</div>
<style>
@keyframes display-animation {
  0% { display: none; }
  100% { display: block; }
}
#target {
  display: none;
}
#target.animate {
  animation: display-animation 1s;
  display: block;
}
</style>
<script>
promise_test(async (t) => {
  t.add_cleanup(() => target.classList.remove('animate'));
  let numAnimationstartFired = 0;
  target.addEventListener('animationstart', () => numAnimationstartFired++);

  assert_equals(getComputedStyle(target).display, 'none',
  'The display should be none before the animation.');

  await waitForAnimationFrames(1);
  target.classList.add('animate');
  await waitForAnimationFrames(2);

  assert_equals(getComputedStyle(target).display, 'block',
    'The display should be block during the animation.');
  assert_equals(numAnimationstartFired, 1,
    'Only one animation should start.');
}, 'display:none animating to display:block should be block for the whole animation.');
</script>