Div(t);

  const animA = div.animate({ opacity: 1 }, { duration: 1, fill: 'forwards' });
  const animB = div.animate({ opacity: 1 }, { duration: 1, fill: 'forwards' });
  await animA.finished;
  // It is not guaranteed that the mircrotask PerformCheckpoint() happens before
  // the animation finish promised got resolved, because the microtask
  // checkpoint could also be triggered from other source such as the event_loop
  // Thus we wait for one animation frame to make sure the finished animation is
  // 