layout-instability/shift-with-counterscroll-2.html

<!DOCTYPE html>
<title>Layout Instability: shift with counterscroll not counted, with 2 scrollers</title>
<link rel="help" href="https://wicg.github.io/layout-instability/" />
<style>
.scroller {
  overflow: scroll;
  position: absolute;
  left: 20px;
  top: 20px;
  width: 200px;
  height: 200px;
}
.content {
  width: 170px;
  height: 600px;
}
.changer {
  position: relative;
  background: yellow;
  left: 10px;
  top: 100px;
  width: 150px;
  height: 150px;
}

</style>
<div id="scroller1" class="scroller">
  <div class="content">
    <div id="changer1" class="changer"></div>
  </div>
</div>
<div id="scroller2" class="scroller">
  <div class="content">
    <div id="changer2" class="changer"></div>
  </div>
</div>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/util.js"></script>
<script>

promise_test(async () => {
  const watcher = new ScoreWatcher;

  // Wait for the initial render to complete.
  await waitForAnimationFrames(2);

  // Top goes from 100 to 200. scroll by 100 to counter it.
  changer1.style.top = "200px";
  scroller1.scrollTop = 100;
  // Top goes from 100 to 300. scroll by 200 to counter it.
  changer2.style.top = "300px";
  scroller2.scrollTop = 200;

  await waitForAnimationFrames(3);
  assert_equals(watcher.score, 0);
}, "Shift with counterscroll not counted, with 2 scrollers.");

</script>