code: func (n *testNode) ControlClient(ctx context.Context) (api.ControlClient, error) {
  	ctx, cancel := context.WithTimeout(ctx, opsTimeout)
  	defer cancel()
  	connChan := n.node.ListenControlSocket(ctx)
  	var controlConn *grpc.ClientConn
  	if err := testutils.PollFuncWithTimeout(nil, func() error {
  		select {
  		case controlConn = <-connChan:
  		default:
  		}
  		if controlConn == nil {
  			return fmt.Errorf("didn't get control api connection")
  		}
  		return nil
  	}, opsTimeout); err != nil {
  		return nil, err
  	}
  	return api.NewControlClient(controlConn), nil
  }
docs: // ControlClient returns grpc client to ControlAPI of node. It will panic for
  // non-manager nodes.