testing/web-platform/tests/layout-instability/simple-block-movement.html


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<!DOCTYPE html>
<title>Layout Instability: simple block movement is detected</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>
#shifter { position: relative; width: 300px; height: 200px; background: blue; }
</style>
<div id="shifter"></div>
<script>

const watcher = new ScoreWatcher;
promise_test(async () => {
  // Wait for the initial render to complete.
  await waitForAnimationFrames(2);

  // Modify the position of the div.
  document.querySelector("#shifter").style = "top: 160px";

  // An element of size (300 x 200) has shifted by 160px.
  const expectedScore = computeExpectedScore(300 * (200 + 160), 160);

  // Observer fires after the frame is painted.
  cls_expect(watcher, {score: 0});
  await watcher.promise;
  cls_expect(watcher, {score: expectedScore});
}, 'Simple block movement.');

</script>