WebKit export of https://bugs.webkit.org/show_bug.cgi?id=235014 (#32301)
diff --git a/css/css-animations/animation-change-underlying-value-changed-in-flight.html b/css/css-animations/animation-change-underlying-value-changed-in-flight.html
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+<!doctype html>
+<meta charset=utf-8>
+<title>Changing the underlying value of an animated property with implicit keyframes</title>
+<link rel="help" href="https://drafts.csswg.org/css-animations/">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+
+@keyframes implicit-from {
+ to { margin-left: 100px }
+}
+
+@keyframes implicit-to {
+ from { margin-left: 100px }
+}
+
+</style>
+<div id="log"></div>
+<script>
+'use strict';
+
+const implicit_keyframe_test = (animationName, offset) => {
+ test(t => {
+ const div = addDiv(t);
+
+ // Set up animation to be paused and be at its mid-way point through easing.
+ div.style.animation = `${animationName} 10s paused steps(2, start)`;
+ const animation = div.getAnimations()[0];
+
+ assert_equals(getComputedStyle(div).marginLeft, "50px", "Computed style before changing the underlying style");
+
+ // Change the underlying value.
+ div.style.marginLeft = "200px";
+ assert_equals(getComputedStyle(div).marginLeft, "150px", "Computed style after changing the underlying style");
+ }, `Changing the underlying value of an animated property with an implicit ${offset}% keyframe`);
+};
+
+implicit_keyframe_test("implicit-from", "0");
+implicit_keyframe_test("implicit-to", "100");
+
+</script>
