chromium/third_party/blink/web_tests/external/wpt/dom/events/scrolling/wheel-event-transactions-target-move.html

<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-actions.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="scroll_support.js"></script>
<style>
body {
  margin: 0;
  padding: 0;
  height: 200vh;
}

.spacer {
  width: 100%;
  height: 25px;
  padding: 0;
  margin: 0;
}

</style>
<head>
<body>
<div id="initialTarget" class="spacer" style="background: red"></div>
<div id="firstRootSpacer" class="spacer" style="background: green"></div>
<div id="secondRootSpacer" class="spacer" style="background: blue"></div>
</body>

<script>

promise_test(async (t) => {
  await new Promise(resolve => addEventListener("load", resolve, {once: true}));

  await waitForCompositorReady();

  await waitForCompositorCommit();

  let wheelEventTargets = [];
  let movedInitialTarget = false;

  // Move the initial element the wheel event is targetted at once we fire the
  // first wheel event, then log the subsequent wheel event targets.
  function moveInitialElement(e) {
    wheelEventTargets.push(e.target);
    if (!movedInitialTarget) {
      movedInitialTarget = true;
      secondRootSpacer.insertAdjacentElement('afterend', e.target);
    }
  }
  window.addEventListener("wheel", moveInitialElement, {passive: true});

  await waitForCompositorCommit();

  await new test_driver.Actions()
    .addWheel("wheel1")
    .scroll(40, 2, 0, 30, {origin: "viewport"})
    .pause(1)
    .scroll(40, 2, 0, 30, {origin: "viewport"})
    .send();

  // TODO(dlrobertson): Use the scrollend event here to wait for the
  // wheel scroll to finish instead of waitForAnimationEnd().
  await waitForAnimationEnd(() => { return document.scrollingElement.scrollTop; });
  await waitForCompositorCommit();

  // The first wheel event should be targetted at the moved element.
  assert_equals(wheelEventTargets.shift(), initialTarget,
                "Initial wheel event has the moved element as the target");

  wheelEventTargets.forEach((wheelEventTarget, i) => {
    // TODO(dlrobertson): This assertion is pretty weak, but browsers seem to disagree
    // on what element the event should target. Find out what the target should be here
    // and make this assertion more restrictive.
    assert_not_equals(wheelEventTarget, initialTarget,
                      "Wheel event at index `" + i + "` targetted the initial element");
  });
  assert_greater_than(document.scrollingElement.scrollTop, 0, "The document has scrolled");
}, "Move the initial wheel event target.");
</script>
</html>