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diff --git a/testing/web-platform/tests/layout-instability/expand-above-viewport.html b/testing/web-platform/tests/layout-instability/expand-above-viewport.html
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+++ b/testing/web-platform/tests/layout-instability/expand-above-viewport.html
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+<!DOCTYPE html>
+<title>Layout Instability: layout shift when content expanded above the viewport</title>
+<link rel="help" href="https://wicg.github.io/layout-instability/" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/test-adapter.js"></script>
+<script src="resources/util.js"></script>
+<style>
+body {
+ margin: 0;
+ /* To avoid browser automatic scroll offset adjustment for the expansion. */
+ overflow-anchor: none;
+}
+</style>
+<div id="expander" style="height: 50vh"></div>
+<div id="shifted" style="width: 300px; height: 300vh; background: blue"></div>
+<script>
+
+promise_test(async () => {
+ const watcher = new ScoreWatcher;
+
+ // Wait for the initial render to complete.
+ await waitForAnimationFrames(2);
+
+ const viewHeight = document.documentElement.clientHeight;
+ window.scrollTo(0, viewHeight);
+
+ await waitForAnimationFrames(2);
+
+ // Expander expands to push |shifted| down.
+ expander.style.height = '150vh';
+
+ const expectedScore1 = computeExpectedScore(300 * viewHeight, viewHeight);
+
+ // Observer fires after the frame is painted.
+ cls_expect(watcher, {score: 0});
+ await watcher.promise;
+ cls_expect(watcher, {score: expectedScore1});
+
+ // Expander expands to push |shifted| out of viewport.
+ expander.style.height = '200vh';
+
+ const expectedScore2 = expectedScore1 +
+ computeExpectedScore(0.5 * 300 * viewHeight, 0.5 * viewHeight);
+ await watcher.promise;
+ cls_expect(watcher, {score: expectedScore2});
+}, "Layout shift when content expanded above the viewport");
+
+</script>