assertThat(exception.cause)
      .isNotNull()
      .matchesPredicate { it is InterruptedException || it is RejectedExecutionException }
    assertThat(clientTestRule.takeUncaughtException())
      .matchesPredicate { it == null || it is RejectedExecutionException }
  }

  private fun sleep(delayMillis: Int) {
    try {
      Thread.sleep(delayMillis.toLong())