// 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();

   *
   * @throws IllegalStateException when the call has already been executed.
   */
  fun enqueue(responseCallback: Callback)

  /** Cancels the request, if possible. Requests that are already complete cannot be canceled. */
  fun cancel()

  /**
   * Returns true if this call has been either [executed][execute] or [enqueued][enqueue]. It is an
   * error to execute a call more than once.
   */
  fun isExecuted(): Boolean

    dispatcher.maxRequests = 2
    client.newCall(newRequest("http://a/1")).enqueue(callback)
    client.newCall(newRequest("http://b/1")).enqueue(callback)
    client.newCall(newRequest("http://c/1")).enqueue(callback)
    client.newCall(newRequest("http://a/2")).enqueue(callback)
    client.newCall(newRequest("http://b/2")).enqueue(callback)
    dispatcher.maxRequests = 4

  }

  /**
   * 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("/")))

  enum WorkerRunningState {
    /** Runnable is not running and not queued for execution */
    IDLE,
    /** Runnable is not running, but is being queued for execution */
    QUEUING,
    /** runnable has been submitted but has not yet begun execution */
    QUEUED,
    RUNNING,
  }

  /** Underlying executor that all submitted Runnable objects are run on. */

      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) {