Problem mocking method through another method

[JJourdan]

Hi,

I've two method that implement Server :
func (s *Server) nrCells
func (s *Server) extractTA

extractTA is being called inside nrCells.
Since I'm testing nrCells, I would like to mock extractTA.

So I tried with the following Mock structure :

type MockServer struct {
	Server
	mock.Mock
}

// Mock implementation of extractTA method.
func (m *MockServer) extractTA(taID string, nrCellList []NrCellData) []NrCellData {
	logger.Info("extractTA called with taID: %s, nrCellList: %+v", taID, nrCellList)
	args := m.Called(taID, nrCellList)
	return args.Get(0).([]NrCellData)
}

func TestNrCells(t *testing.T) {
	mockServer := new(MockServer)
	t.Run("Valid ta-id parameter", func(t *testing.T) {
		mockTAID := "123"
		mockNrCellData := []NrCellData{myData}
		mockServer.On("extractTA", mock.Anything, mock.Anything).Return(mockNrCellData)
		req, err := http.NewRequest("GET", myRequest + " [ " + mockTAID+"]", http.NoBody)
		assert.NoError(t, err)
		rr := httptest.NewRecorder()
		handler := http.HandlerFunc(mockServer.nrCells)
		handler.ServeHTTP(rr, req)

		assert.Equal(t, http.StatusOK, rr.Code)

		var response []NrCellData
		err = json.Unmarshal(rr.Body.Bytes(), &response)
		assert.NoError(t, err)

		assert.Equal(t, mockNrCellData, response)
		mockServer.AssertExpectations(t)
	})

This is not working, I can see extractTA logs, so it's not mocked (and causing panic because of that).
But I also tried a direct call to test the mock :

mockServer.On("extractTA", mock.Anything, mock.Anything).Return(mockNrCellData)
response := mockServer.extractTA(...)
assert.Equal(t, mockNrCellData, response)

And this is working well.
There's something wrong when I'm calling it through nrCells.
Question : Is it possible to do what I'm trying to do ? Mock a method called from another method from the same MockObject.
If yes : what's wrong here ?
If not : do I have another to reach my goal ?

Thanks

[brackendawson]

I would say that in my opinion this highlights a problem in the code, not the test. If you need to mock one method of a class to test another method of the class I would suggest that they do not belong in the same class. Does Server have too many responsibilities? Consider your hexagonal architecture.

Can extractTA be moved to a separate class? Rather than:

type Server struct{}
func (s *Server) nrCells {
    s.extractTA()
}
func (s *Server) extractTA {}

Consider:

type TAExtractor interface{
    extractTA()
}
type Server struct{
    TAExtractor
}
func (s *Server) nrCells {
   s.extractTA()
}

Note that this is not inheritance, your implementation of extractTA will have no access to Server.

It's not possible to write the test you want with testify. You'd need to use monkey patching, which is not safe.