redQueue.cancelAll()
    assertThat(taskFaker.executeCallCount).isEqualTo(1)

    blueQueue.cancelAll()
    assertThat(taskFaker.executeCallCount).isEqualTo(1)
  }

  @Test fun noMoreThanOneWorkerThreadWaitingToStartAtATime() {
    // Enqueueing the red task starts a thread because the head of the queue changed.
    redQueue.execute("red task") {
      log += "red:starting@${taskFaker.nanoTime}"
      taskFaker.sleep(100.µs)