public Reaper(Engine engine) {
    _engine = engine;
  }
@Test
  public void testReaper()
      throws InterruptedException {
    final int COUNT = 10;
    final List<Reaper.Zombie> zombies = new ArrayList<>();
    final CountDownLatch latch = new CountDownLatch(COUNT);

    for (int i = 0; i < COUNT; ++i) {
      zombies.add(() -> Task.action("countDown", () -> latch.countDown()));
    }

    zombies.forEach(z -> _reaper.submit(z));
    Assert.assertTrue(latch.await(10, TimeUnit.SECONDS));
  }