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+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Playing an animation</title>
+<link rel="help"
+      href="https://drafts.csswg.org/web-animations/#playing-an-animation-section">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+test(t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.currentTime = 1 * MS_PER_SEC;
+  assert_time_equals_literal(animation.currentTime, 1 * MS_PER_SEC);
+  animation.play();
+  assert_time_equals_literal(animation.currentTime, 1 * MS_PER_SEC);
+}, 'Playing a running animation leaves the current time unchanged');
+
+test(t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.finish();
+  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
+  animation.play();
+  assert_time_equals_literal(animation.currentTime, 0);
+}, 'Playing a finished animation seeks back to the start');
+
+test(t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.playbackRate = -1;
+  animation.currentTime = 0;
+  assert_time_equals_literal(animation.currentTime, 0);
+  animation.play();
+  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
+}, 'Playing a finished and reversed animation seeks to end');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.finish();
+
+  // Initiate a pause then abort it
+  animation.pause();
+  animation.play();
+
+  // Wait to return to running state
+  await animation.ready;
+
+  assert_true(animation.currentTime < 100 * 1000,
+              'After aborting a pause when finished, the current time should'
+              + ' jump back to the start of the animation');
+}, 'Playing a pause-pending but previously finished animation seeks back to'
+   + ' to the start');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.finish();
+  await animation.ready;
+
+  animation.play();
+  assert_equals(animation.startTime, null, 'start time is unresolved');
+}, 'Playing a finished animation clears the start time');
+
+test(t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.cancel();
+  const promise = animation.ready;
+  animation.play();
+  assert_not_equals(animation.ready, promise);
+}, 'The ready promise should be replaced if the animation is not already'
+   + ' pending');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  const promise = animation.ready;
+  const promiseResult = await promise;
+  assert_equals(promiseResult, animation);
+  assert_equals(animation.ready, promise);
+}, 'A pending ready promise should be resolved and not replaced when the'
+   + ' animation enters the running state');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.currentTime = 50 * MS_PER_SEC;
+  await animation.ready;
+
+  animation.pause();
+  await animation.ready;
+
+  const holdTime = animation.currentTime;
+
+  animation.play();
+  await animation.ready;
+
+  assert_less_than_equal(
+    animation.startTime,
+    animation.timeline.currentTime - holdTime + TIME_PRECISION
+  );
+}, 'Resuming an animation from paused calculates start time from hold time');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  await animation.ready;
+
+  // Go to pause-pending state
+  animation.pause();
+  assert_true(animation.pending, 'Animation is pending');
+  const pauseReadyPromise = animation.ready;
+
+  // Now play again immediately (abort the pause)
+  animation.play();
+  assert_true(animation.pending, 'Animation is still pending');
+  assert_equals(animation.ready, pauseReadyPromise,
+                'The pause Promise is re-used when playing while waiting'
+                + ' to pause');
+
+  // Sanity check: Animation proceeds to running state
+  await animation.ready;
+  assert_true(!animation.pending && animation.playState === 'running',
+              'Animation is running after aborting a pause');
+}, 'If a pause operation is interrupted, the ready promise is reused');
+
+promise_test(async t => {
+  // Seek animation beyond target end
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.currentTime = -100 * MS_PER_SEC;
+  await animation.ready;
+
+  // Set pending playback rate to the opposite direction
+  animation.updatePlaybackRate(-1);
+  assert_true(animation.pending);
+  assert_equals(animation.playbackRate, 1);
+
+  // When we play, we should seek to the target end, NOT to zero (which
+  // is where we would seek to if we used the playbackRate of 1.
+  animation.play();
+  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
+}, 'A pending playback rate is used when determining auto-rewind behavior');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.cancel();
+  assert_equals(animation.startTime, null,
+                'Start time should be unresolved');
+
+  const playTime = animation.timeline.currentTime;
+  animation.play();
+  assert_true(animation.pending, 'Animation should be play-pending');
+
+  await animation.ready;
+
+  assert_false(animation.pending, 'animation should no longer be pending');
+  assert_time_greater_than_equal(animation.startTime, playTime,
+                      'The start time of the playing animation should be set');
+}, 'Playing a canceled animation sets the start time');
+
+promise_test(async t => {
+  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  animation.playbackRate = -1;
+  animation.cancel();
+  assert_equals(animation.startTime, null,
+                'Start time should be unresolved');
+
+  const playTime = animation.timeline.currentTime;
+  animation.play();
+  assert_true(animation.pending, 'Animation should be play-pending');
+
+  await animation.ready;
+
+  assert_false(animation.pending, 'Animation should no longer be pending');
+  assert_time_greater_than_equal(animation.startTime, playTime + 100 * MS_PER_SEC,
+                      'The start time of the playing animation should be set');
+}, 'Playing a canceled animation backwards sets the start time');
+
+</script>
+</body>