code: func (t *Transport) HealthCheck(ctx context.Context, id uint64) error {
  	t.mu.Lock()
  	p, ok := t.peers[id]
  	t.mu.Unlock()
  	if !ok {
  		return ErrIsNotFound
  	}
  	ctx, cancel := t.withContext(ctx)
  	defer cancel()
  	return p.healthCheck(ctx)
  }
docs: // HealthCheck checks health of particular peer.