code: func (h *Heartbeat) ForceSend(timeout time.Duration) error {
  	timeoutC := time.After(timeout)
  	select {
  	case h.sendC <- struct{}{}:
  	case <-timeoutC:
  		return trace.ConnectionProblem(nil, "timeout waiting for send")
  	}
  	select {
  	case <-h.announceC:
  		return nil
  	case <-timeoutC:
  		return trace.ConnectionProblem(nil, "timeout waiting for announce to be sent")
  	}
  }
docs: // ForceSend forces send cycle, used in tests, returns
  // nil in case of success, error otherwise