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diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html
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index 0000000000..1fe354edfd
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+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#avoiding-cycles">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  #scroller {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+    scroll-timeline: timeline;
+  }
+  #contents {
+    height: 200px;
+  }
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+  #element {
+    width: 0px;
+    animation: expand 10s linear;
+    animation-timeline: timeline;
+  }
+  /* Ensure stable expectations if feature is not supported */
+  @supports not (animation-timeline:foo) {
+    #element { animation-play-state: paused; }
+  }
+</style>
+<div id=scroller>
+  <div id=contents></div>
+</div>
+<div id=element></div>
+<script>
+  promise_test(async (t) => {
+    // The scroll timeline is initially inactive until the first frame.
+    assert_equals(getComputedStyle(element).width, '0px');
+    await waitForNextFrame();
+    scroller.scrollTop = 50;
+    // Scrolling position should not yet be reflected in the animation,
+    // since the new scroll position has not yet been sampled.
+    assert_equals(getComputedStyle(element).width, '100px');
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '150px');
+  }, 'Scroll position is sampled once per frame');
+</script>