code: func (m *MockEndorserServer) ProcessProposal(context context.Context,
  	proposal *pb.SignedProposal) (*pb.ProposalResponse, error) {
  	if m.ProposalError == nil {
  		return &pb.ProposalResponse{Response: &pb.Response{
  			Status: 200,
  		}, Endorsement: &pb.Endorsement{Endorser: []byte("endorser"), Signature: []byte("signature")},
  			Payload: m.createProposalResponsePayload()}, nil
  	}
  	return &pb.ProposalResponse{Response: &pb.Response{
  		Status:  500,
  		Message: m.ProposalError.Error(),
  	}}, m.ProposalError
  }
docs: // ProcessProposal mock implementation that returns success if error is not set
  // error if it is