fun advanceUntil(newTime: Long) {
    taskRunner.assertLockNotHeld()

    taskRunner.withLock {
      check(currentTask == TestThreadSerialTask)
      nanoTime = newTime
      yieldUntil(ResumePriority.AfterOtherTasks)
    }
  }

  /** Confirm all tasks have completed. Used by the test thread only. */
  fun assertNoMoreTasks() {
    taskRunner.assertLockNotHeld()

    taskRunner.withLock {