code: func (sn *SimNode) Client() (*rpc.Client, error) {
  	sn.lock.RLock()
  	defer sn.lock.RUnlock()
  	if sn.client == nil {
  		return nil, errors.New("node not started")
  	}
  	return sn.client, nil
  }
docs: // Client returns an rpc.Client which can be used to communicate with the
  // underlying services (it is set once the node has started)