* #enqueue enqueued} and {@link #dispatch dispatched}.
   */
  public void addListener(L listener, Executor executor) {
    checkNotNull(listener, "listener");
    checkNotNull(executor, "executor");
    listeners.add(new PerListenerQueue<>(listener, executor));
  }

  /**
   * Enqueues an event to be run on currently known listeners.
   *

    }

    if (failFastResponse != null && responseQueue.peek() == null) {
      // Fail fast if there's no response queued up.
      return failFastResponse!!
    }

    val result = responseQueue.take()

    // If take() returned because we're shutting down, then enqueue another dead letter so that any
    // other threads waiting on take() will also return.
    if (result == DEAD_LETTER) responseQueue.add(DEAD_LETTER)

  private val messageAndCloseQueue = ArrayDeque<Any>()

  /** The total size in bytes of enqueued but not yet transmitted messages. */
  private var queueSize = 0L

  /** True if we've enqueued a close frame. No further message frames will be enqueued. */
  private var enqueuedClose = false

  /** The close code from the peer, or -1 if this web socket has not yet read a close frame. */

  // instance for every unit test.
  MockWebServer server = new MockWebServer();

  // Schedule some responses.
  server.enqueue(new MockResponse.Builder()
      .body("hello, world!")
      .build());
  server.enqueue(new MockResponse.Builder()
      .body("sup, bra?")
      .build());
  server.enqueue(new MockResponse.Builder()
      .body("yo dog")
      .build());

  // Start the server.
  server.start();

  }

  /**
   * Test that MockWebServer blocks for a call to enqueue() if a request is made before a mock
   * response is ready.
   */
  @Test
  fun dispatchBlocksWaitingForEnqueue() {
    Thread {
      try {
        Thread.sleep(1000)
      } catch (ignored: InterruptedException) {
      }
      server.enqueue(MockResponse().setBody("enqueued in the background"))
    }.start()

    /**
     * Used to update and read the latestTaskQueue field. Set to null once the runnable has been run
     * or queued.
     */
    @Nullable ExecutionSequencer sequencer;

    /**
     * Executor the task was set to run on. Set to null when the task has been queued, run, or
     * cancelled.
     */
    @Nullable Executor delegate;

    /**

   * Test that MockWebServer blocks for a call to enqueue() if a request is made before a mock
   * response is ready.
   */
  @Test
  fun dispatchBlocksWaitingForEnqueue() {
    Thread {
      try {
        Thread.sleep(1000)
      } catch (ignored: InterruptedException) {
      }
      server.enqueue(
        MockResponse
          .Builder()
          .body("enqueued in the background")
          .build(),

        }
    }
  }

  companion object {
    /**
     * Enqueues a [Call] and process it as [EventSource] with [listener].
     */
    @JvmStatic
    @JvmName("enqueue")
    fun Call.enqueueEventSource(listener: EventSourceListener): EventSource = RealEventSource(this, listener).also(this::enqueue)

    /**
     * Processes the existing response with [listener].
     */
    @JvmStatic

    // makeSimpleCall() because it uses the MockResponse enqueued above.
    val callB = client.newCall(Request(server.url("/")))
    callB.execute().use { response ->
      assertThat(response.body.string()).isEqualTo("abc")
    }
  }

  private fun makeSimpleCall() {
    server.enqueue(MockResponse(body = "healthy"))
    val callB = client.newCall(Request(server.url("/")))

      if (existingCall.host == host) return existingCall
    }
    return null
  }

  /**
   * Cancel all calls currently enqueued or executing. Includes calls executed both
   * [synchronously][Call.execute] and [asynchronously][Call.enqueue].
   */
  @Synchronized
  fun cancelAll() {
    for (call in readyAsyncCalls) {
      call.call.cancel()
    }
    for (call in runningAsyncCalls) {