object : TaskRunner.Backend {
        override fun execute(
          taskRunner: TaskRunner,
          runnable: Runnable,
        ) {
          taskRunner.assertLockHeld()

          val queuedTask = RunnableSerialTask(runnable)
          serialTaskQueue += queuedTask
          executeCallCount++
          isParallel = serialTaskQueue.size > 1
        }

        override fun nanoTime() = nanoTime