if (readyQueues.isEmpty()) {
        return null // Nothing to do.
      }

      val now = backend.nanoTime()
      var minDelayNanos = Long.MAX_VALUE
      var readyTask: Task? = null
      var multipleReadyTasks = false

      // Decide what to run. This loop's goal wants to:
      //  * Find out what this thread should do (either run a task or sleep)

    contextSwitchCount++
    nextTask.start()
    return nextTask
  }

  private interface SerialTask {
    /** Returns true if this task is ready to start. */
    fun isReady() = true

    /** Do this task's work, and then start another, such as by calling [startNextTask]. */
    fun start()
  }

  private object TestThreadSerialTask : SerialTask {
    override fun start() = error("unexpected call")
  }

    )
  }

  /** Test the introspection method [TaskQueue.scheduledTasks]. */
  @Test fun scheduledTasks() {
    redQueue.execute("task one", 100.µs) {
      // Do nothing.
    }

    redQueue.execute("task two", 200.µs) {
      // Do nothing.
    }

    assertThat(redQueue.scheduledTasks.toString()).isEqualTo("[task one, task two]")

    assertThat(testLogHandler.takeAll()).containsExactly(