css/css-layout-api/sync-layout-microtasks.https.html

<!DOCTYPE html>
<html>
<link rel="help" href="https://drafts.css-houdini.org/css-layout-api/#invoke-a-layout-callback">
<meta name="assert" content="This test checks running the microtask queue for a layout() class won't run the main world's microtask queue." />
<style>
#test {
  display: layout(child-layout);
  width: 100px;
}

#test > div {
  height: 100px;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/common/worklet-reftest.js"></script>

<div id="test">
  <div></div>
</div>

<script id="code" type="text/worklet">
registerLayout('child-layout', class {
  async intrinsicSizes() {}
  async layout([child]) {
    const fragment = await child.layoutNextFragment();
    return {autoBlockSize: 50, childFragments: [fragment]};
  }
});
</script>

<script>
promise_test(async t => {
  if (typeof CSS.layoutWorklet === 'undefined') {
    throw Error('CSS Layout API not supported.');
  }

  await importWorklet(CSS.layoutWorklet, document.getElementById('code').textContent);

  let resolved = false;
  let p = Promise.resolve().then(() => {
    resolved = true;
  });
  assert_false(resolved);

  // Running the layout-worklet's microtask queue shouldn't trigger the main
  // world's microtask queue.
  assert_equals(document.getElementById('test').clientHeight, 50);
  assert_false(resolved);

  await p;
  assert_true(resolved);
});
</script>
</html>