code: func (c *MockClock) advanceTo(end time.Time) {
  	for {
  		t := c.nextWakeupTime()
  		if t == (time.Time{}) || t.After(end) {
  			break
  		}
  		c.advanceToNextWakeup()
  	}
  	c.now = end
  }
docs: // This assumes c.mutex is locked