code: func (f *NodeClient) NodeExpandVolume(ctx context.Context, req *csipb.NodeExpandVolumeRequest, opts ...grpc.CallOption) (*csipb.NodeExpandVolumeResponse, error) {
  	if f.nextErr != nil {
  		return nil, f.nextErr
  	}
  
  	if req.GetVolumeId() == "" {
  		return nil, errors.New("missing volume id")
  	}
  	if req.GetVolumePath() == "" {
  		return nil, errors.New("missing volume path")
  	}
  
  	if req.GetCapacityRange().RequiredBytes <= 0 {
  		return nil, errors.New("required bytes should be greater than 0")
  	}
  
  	resp := &csipb.NodeExpandVolumeResponse{
  		CapacityBytes: req.GetCapacityRange().RequiredBytes,
  	}
  	return resp, nil
  }
docs: // NodeExpandVolume implements csi method