https://github.com/facebook/react/blob/30b47103d4354d9187dc0f1fb804855a5208ca9f/packages/scheduler/src/Scheduler.js#L180-L185
Scheduler.unstable_yieldValue('Low: ' + inferPriorityFromCallstack()),
      );
      scheduleCallback(IdlePriority, () =>
        Scheduler.unstable_yieldValue('Idle: ' + inferPriorityFromCallstack()),
      );
      expect(Scheduler).toFlushAndYield([
        'Immediate: ' + ImmediatePriority,
        'UserBlocking: ' + UserBlockingPriority,
        'Normal: ' + NormalPriority,
        'Low: ' + LowPriority,
        'Idle: ' + IdlePriority,
      ]);
    });
  }
  describe('delayed tasks', () => {
    it('schedules a delayed task', () => {
      scheduleCallback(
        NormalPriority,
        () => Scheduler.unstable_yieldValue('A'),
        {
          delay: 1000,
        },
      );
      
      expect(Scheduler).toFlushAndYield([]);
      
      Scheduler.unstable_advanceTime(999);
      
      expect(Scheduler).toFlushAndYield([]);