public void testElement_empty() {
    try {
      getQueue().element();
      fail("emptyQueue.element() should throw");
    } catch (NoSuchElementException expected) {
    }
    expectUnchanged();
  }

  @CollectionSize.Require(ONE)
  public void testElement_size1() {
    assertEquals("size1Queue.element() should return first element", e0(), getQueue().element());
    expectUnchanged();
  }

  @CollectionSize.Require(ZERO)
  public void testPeek_empty() {
    assertNull("emptyQueue.peek() should return null", getQueue().peek());
    expectUnchanged();
  }

  @CollectionSize.Require(ONE)
  public void testPeek_size1() {
    assertEquals("size1Queue.peek() should return first element", e0(), getQueue().peek());
    expectUnchanged();
  }

  @CollectionFeature.Require(KNOWN_ORDER)
  @CollectionSize.Require(SEVERAL)

  public void testOffer_supportedNotPresent() {
    assertTrue("offer(notPresent) should return true", getQueue().offer(e3()));
    expectAdded(e3());
  }

  @CollectionFeature.Require({SUPPORTS_ADD, ALLOWS_NULL_VALUES})
  public void testOffer_nullSupported() {
    assertTrue("offer(null) should return true", getQueue().offer(null));
    expectAdded((E) null);
  }

  @CollectionSize.Require(ZERO)
  public void testPeek_empty() {
    assertNull("emptyQueue.peek() should return null", getQueue().peek());
    expectUnchanged();
  }

  @CollectionSize.Require(ONE)
  public void testPeek_size1() {
    assertEquals("size1Queue.peek() should return first element", e0(), getQueue().peek());
    expectUnchanged();
  }

  @CollectionFeature.Require(KNOWN_ORDER)
  @CollectionSize.Require(SEVERAL)

    try {
      getQueue().remove();
      fail("emptyQueue.remove() should throw");
    } catch (NoSuchElementException expected) {
    }
    expectUnchanged();
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testRemove_size1() {
    assertEquals("size1Queue.remove() should return first element", e0(), getQueue().remove());
    expectMissing(e0());
  }

  public void testPoll_empty() {
    assertNull("emptyQueue.poll() should return null", getQueue().poll());
    expectUnchanged();
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testPoll_size1() {
    assertEquals("size1Queue.poll() should return first element", e0(), getQueue().poll());
    expectMissing(e0());
  }

  private val taskRunner = TaskRunner(backend)
  private val queue = taskRunner.newQueue()

  @AfterEach fun tearDown() {
    backend.shutdown()
  }

  @Test fun test() {
    val t1 = System.nanoTime() / 1e6

    val delays = mutableListOf(TimeUnit.MILLISECONDS.toNanos(1000), -1L)
    queue.schedule("task", TimeUnit.MILLISECONDS.toNanos(750)) {
      log.put("runOnce delays.size=${delays.size}")

  public void testPoll_empty() {
    assertNull("emptyQueue.poll() should return null", getQueue().poll());
    expectUnchanged();
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testPoll_size1() {
    assertEquals("size1Queue.poll() should return first element", e0(), getQueue().poll());
    expectMissing(e0());
  }

    serverSocket.close()

    // Await shutdown.
    for (queue in taskRunner.activeQueues()) {
      if (!queue.idleLatch().await(5, TimeUnit.SECONDS)) {
        throw IOException("Gave up waiting for queue to shut down")
      }
    }
    taskRunnerBackend.shutdown()
  }

  private fun serveConnection(raw: Socket) {
    taskRunner.newQueue().execute("MockWebServer ${raw.remoteSocketAddress}", cancelable = false) {

  private final Executor executor;

  @GuardedBy("queue")
  private final Deque<Runnable> queue = new ArrayDeque<>();

  /** see {@link WorkerRunningState} */
  @LazyInit
  @GuardedBy("queue")
  private WorkerRunningState workerRunningState = IDLE;

  /**
   * This counter prevents an ABA issue where a thread may successfully schedule the worker, the
   * worker runs and exhausts the queue, another thread enqueues a task and fails to schedule the