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+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Reversing an animation</title>
+<link rel="help"
+      href="https://drafts.csswg.org/web-animations/#reversing-an-animation-section">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="testcommon.js"></script>
+<style>
+.scroller {
+  overflow: auto;
+  height: 100px;
+  width: 100px;
+  will-change: transform;
+}
+
+.contents {
+  height: 1000px;
+  width: 100%;
+}
+</style>
+<body>
+<script>
+'use strict';
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.reverse();
+  animation.currentTime = CSSNumericValue.parse("40%");
+  await animation.ready;
+  assert_percents_equal(animation.currentTime, 40);
+}, 'Setting current time while reverse-pending preserves currentTime');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  await animation.ready;
+
+  animation.currentTime = CSSNumericValue.parse("50%");
+  const previousPlaybackRate = animation.playbackRate;
+  animation.reverse();
+  assert_equals(animation.playbackRate, previousPlaybackRate,
+                'Playback rate should not have changed');
+  await animation.ready;
+
+  assert_equals(animation.playbackRate, -previousPlaybackRate,
+                'Playback rate should be inverted');
+}, 'Reversing an animation inverts the playback rate');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  animation.currentTime = CSSNumericValue.parse("40%");
+  await animation.ready;
+  assert_percents_equal(animation.startTime, -40);
+  assert_percents_equal(animation.currentTime, 40);
+
+  animation.reverse();
+  await animation.ready;
+  assert_percents_equal(animation.startTime, 100);
+  assert_percents_equal(animation.currentTime, 100);
+}, 'Reversing an animation resets a sticky start time.');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  assert_true(animation.pending,
+              'The animation is pending before we call reverse');
+
+  animation.reverse();
+
+  assert_true(animation.pending,
+              'The animation is still pending after calling reverse');
+}, 'Reversing an animation does not cause it to leave the pending state');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  let readyResolved = false;
+  animation.ready.then(() => { readyResolved = true; });
+
+  animation.reverse();
+
+  await Promise.resolve();
+  assert_false(readyResolved,
+               'ready promise should not have been resolved yet');
+}, 'Reversing an animation does not cause it to resolve the ready promise');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  animation.playbackRate = -1;
+  animation.reverse();
+  await animation.ready;
+
+  assert_percents_equal(animation.currentTime, 0);
+}, 'Reversing an animation with a negative playback rate should cause ' +
+   'the animation to play in a forward direction');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  animation.playbackRate = 0;
+  animation.currentTime = CSSNumericValue.parse("50%");
+  animation.reverse();
+
+  await animation.ready;
+  assert_equals(animation.playbackRate, 0,
+      'reverse() should preserve playbackRate if the playbackRate == 0');
+  assert_percents_equal(animation.currentTime, 0,
+      'Anchors to range start boundary when playback rate is zero');
+}, 'Reversing when when playbackRate == 0 should preserve the playback rate');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  assert_equals(animation.currentTime, null);
+
+  animation.reverse();
+  await animation.ready;
+
+  assert_percents_equal(animation.startTime, 100,
+                        'animation.startTime should be at its effect end');
+  assert_percents_equal(animation.currentTime, 100,
+                        'animation.currentTime should be at its effect end');
+}, 'Reversing an idle animation aligns startTime with the rangeEnd boundary');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  const scroller = animation.timeline.source;
+  // Make the scroll timeline inactive.
+  scroller.style.overflow = 'visible';
+  scroller.scrollTop;
+  await waitForNextFrame();
+
+  assert_throws_dom('InvalidStateError', () => { animation.reverse(); });
+}, 'Reversing an animation without an active timeline throws an ' +
+   'InvalidStateError');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  animation.currentTime = CSSNumericValue.parse("50%");
+  animation.pause();
+  await animation.ready;
+
+  animation.reverse();
+  assert_equals(animation.playState, 'running',
+                'Animation.playState should be "running" after reverse()');
+}, 'Reversing an animation plays a pausing animation');
+
+promise_test(async t => {
+  const animation = createScrollLinkedAnimation(t);
+  animation.play();
+  await animation.ready;
+
+  animation.updatePlaybackRate(2);
+  animation.reverse();
+
+  await animation.ready;
+  assert_equals(animation.playbackRate, -2);
+}, 'Reversing should use the negative pending playback rate');
+</script>
+</body>