[aleksiy123]

Mocks are especially useful when you want to test code heavy with dependency injection.

I like to say that normal tests where you test by passing in params and assert the result is outside in testing.

Mocking is inside out test. Follows naturally from dependency inversion of di. You want to assert your function is making the right calls/params to it's dependencies interfaces from inside.

In your contrived example there is not much value in knowing whether "ns:key" or "key" was used. But if you those are params to some external RPC suddenly this actually becomes pretty useful.

Providing working fakes for every dependency isn't always realistic.

Should I really spend time building a fake of Stripe. Or should I just assert the request I am making to it are the expected ones.

TLDR: I only saw the value of mocks when testing DI server code with many external service dependencies.

[randomdata]

> Providing working fakes for every dependency isn't always realistic.

I don't know what a fake is. Is that what mockery gives you? Per the dictionary, fake is defined similar to mock, but without the no deception condition, so I suppose that adds up.

There are also stubs, which is defined as something that is truncated or a part of. Which, as it pertains to software, is an implementation that implements some kind of bare minimum to satisfy the interface – often returning canned responses, for example. Mockery arguably also fits here, except the assertion part, which is something else. But I guess that's where fake comes in to draw that differentiation?

> But if you those are params to some external RPC suddenly this actually becomes pretty useful.

Sure, a stub might check the inputs and return an error if some condition is not met, without needing to implement the service in full. This remains true to what the real service would also do.

But that's not what mockery does. It just blows up spectacularly if something wasn't right. That doesn't really make any sense. That is now how the real implementation works. Not only that, but in the case of mockery, its documentation advises that you put the dependency logic in the test. How silly is that? Now when you replace Stripe with Line all your tests are broken. If you used a stub, you merely change the stub to match and you're good to go. This way the tests remain pure, as they need to as they are the contract you make with your users. Changing the contract is unacceptable.

And for all that, it doesn't seem to serve any purpose. But we did ask the other guy for a concrete example (i.e. code) to show where one would want to use it. Looking forward to it.

[aleksiy123]

Here, I'll provide an example I generated with chatgpt with some prompting.

    type Server struct {
        Payment         services.PaymentService
        Storage         services.StorageService
        Quota           services.QuotaService
        Auth            services.AuthService
        Notification    services.NotificationService
    }

    // TransactionRequest is the request structure for a purchase
    type TransactionRequest struct {
        UserID    string  `json:"user_id"`
        AuthToken string  `json:"auth_token"`
        ProductID string  `json:"product_id"`
        Price     float64 `json:"price"`
        Currency  string  `json:"currency"`
        File      []byte  `json:"file"`
        Key       string  `json:"key"`
    }

    // TransactionResponse is the response structure after processing a transaction
    type TransactionResponse struct {
        Status  string `json:"status"`
        Message string `json:"message"`
    }

    // HandleTransaction handles the incoming transaction request
    func (s *Server) HandleTransaction(w http.ResponseWriter, r *http.Request) {
        var req TransactionRequest
        if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
            http.Error(w, "invalid request", http.StatusBadRequest)
            return
        }

        // Authenticate user
        userID, err := s.Auth.Authenticate(req.AuthToken)
        if err != nil {
            http.Error(w, "authentication failed", http.StatusUnauthorized)
            return
        }

        // Check and update quota
        allowed, err := s.Quota.CheckQuota(userID)
        if err != nil || !allowed {
            http.Error(w, "quota exceeded", http.StatusForbidden)
            return
        }
        s.Quota.UpdateQuota(userID, 1)  // Assume updating quota by 1 unit per transaction

        // Process payment
        transactionID, err := s.Payment.Charge(req.Price, req.Currency, "payment-token")
        if err != nil {
            http.Error(w, "payment failed", http.StatusInternalServerError)
            return
        }

        // Upload file to S3
        fileURL, err := s.Storage.Upload(req.File, userID + "-files", req.Key)
        if err != nil {
            http.Error(w, "file upload failed", http.StatusInternalServerError)
            return
        }

        // Send notification
        notificationMessage := "Your purchase has been processed successfully."
        s.Notification.SendNotification(userID, notificationMessage)

        response := TransactionResponse{
            Status:  "success",
            Message: "Transaction processed successfully: " + transactionID + " File uploaded to: " + fileURL,
        }
        w.Header().Set("Content-Type", "application/json")
        json.NewEncoder(w).Encode(response)
    }

It is still contrived obviously. But what I would like to show what happens if use stubs. You could pass anything into the dependency parameters and the test would pass. Mock allows you to "lock" in the implementation. Its tightly coupled yes but sometimes that is exactly what you want.

In this example that would be the userId, the bucket name, the key.

Mock allows you inject faults in the test setup. Lets say I want to test the error handling logic. I could do it with multiple types of stubs but if you squint its starting to look the same.

On the topic of Fake vs Stub vs Mock. Real or Fake is the ideal solution here but not always viable due to time/practical constraints. Stubs can be useful but don't give you fine grained control.

[randomdata]

> You could pass anything into the dependency parameters and the test would pass.

I don't follow. Under no circumstance would the test pass under invalid inputs, be it whether you use mocks, stubs, or even mockery (fakes?).

- Obviously it cannot pass while using mocks – a mock matches the real thing to every last detail. If it will fail while using the real thing, it will fail here as well.

- Obviously it cannot pass while using stubs – a stub matches the real thing, partially, to at least the minimum amount necessary for the sake of testing. If it will fail while using the real thing, it will fail here as well.

- Obviously it cannot pass while using mockery – mockery does not match the real thing in any way, but does require you to specify matching inputs with failure when they don't match. If it will fail while using the real thing, it will fail here as well.

I don't know what you are imagining, but I'm not convinced it is a thing. I mean, you could make it a thing - you can do anything your little heart desires, but there would be no reason to ever make it a thing.

Maybe we need some concrete tests to better illustrate what you are talking about?

[aleksiy123]

We seem to be using different definitions of stub and fake. What you call a stub is generally known as a Fake.

https://stackoverflow.com/questions/3459287/whats-the-differ...

Stubs do not react based on their input parameters. However, even fakes have the issue of fault injection.

I don't want to just test valid inputs. I want to make sure I pass the correct inputs for the request parameters through to the dependencies. If pass 100.00 in the request but in my impl I pass 0.00 to the stub. The test will pass because the input is valid. But the implementation is not correct.

Also, mockery is just an alternative mocking api. There is nothing special here.

How would you test the case where the quota update fails with a stub? Here is mockery example again generated with chatgpt.

    func TestHandleTransaction_QuotaUpdateFails(t *testing.T) {
      // Create the mock services
      mockAuth := new(mocks.AuthService)
      mockPayment := new(mocks.PaymentService)
      mockStorage := new(mocks.StorageService)
      mockQuota := new(mocks.QuotaService)
      mockNotification := new(mocks.NotificationService)

      // Setup expectations
      mockAuth.On("Authenticate", mock.Anything).Return("12345", nil)
      mockQuota.On("CheckQuota", "12345").Return(true, nil)  // Quota check passes
      mockQuota.On("UpdateQuota", "12345", mock.AnythingOfType("int64")).Return(errors.New("quota update failed"))  // Quota update fails
      // No need to mock payment and storage as they should not be called if quota update fails

      // Create the server with mock services
      server := &Server{
          Auth:            mockAuth,
          Payment:         mockPayment,
          Storage:         mockStorage,
          Quota:           mockQuota,
          Notification:    mockNotification,
      }

      // Create a test request
      transaction := TransactionRequest{
          UserID:    "12345",
          AuthToken: "valid-token",
          ProductID: "product123",
          Price:     100.0,
          Currency:  "USD",
          File:      []byte("file data"),
      }
      requestBody, _ := json.Marshal(transaction)
      request := httptest.NewRequest(http.MethodPost, "/transaction", bytes.NewReader(requestBody))
      responseRecorder := httptest.NewRecorder()

      // Call the endpoint
      server.HandleTransaction(responseRecorder, request)

      // Check the results
      assert.Equal(t, http.StatusInternalServerError, responseRecorder.Code)
      response := TransactionResponse{}
      json.NewDecoder(responseRecorder.Body).Decode(&response)
      assert.Equal(t, "error", response.Status)
      assert.Contains(t, response.Message, "quota update failed")

      // Assert that all expectations were met
      mockAuth.AssertExpectations(t)
      mockQuota.AssertExpectations(t)
      // Assert no calls to payment and storage
      mockPayment.AssertNotCalled(t, "Charge", mock.AnythingOfType("float64"), mock.AnythingOfType("string"), mock.AnythingOfType("string"))
      mockStorage.AssertNotCalled(t, "Upload", mock.AnythingOfType("[]uint8"), "bucket-name", "key-name")
      // No notification should be sent
      mockNotification.AssertNotCalled(t, "SendNotification", "12345", mock.AnythingOfType("string"))
    }

[randomdata]

> What you call a stub is generally known as a Fake.

I willingly accept your unconventional usage if it greases discussion, but the dictionary is right there. It records how most people use words. What mockery gives appears to be what most people consider a fake. It clearly does not fit the definition of mock. It arguably matches the definition of stub and I think you could reasonably call it that, but I posit that doesn't tell the whole story, which is no doubt why fake emerged.

That said, I don't know what your definitions are. You seem to flail around with them.

> Stubs do not react based on their input parameters.

All of mocks, stubs, and fakes react based on input...

> How would you test the case where the quota update fails with a stub?

... Although this seems like a poor example. It is not clear if the failure state is due to invalid input or due to some other issue.

This, I must say, makes for a really bad test. Tests are, first and foremost, the contract and documentation for your users. They are written so that other people can learn about the system and know what they can depend on during use. The self-validation offered by testing is there merely to ensure that what is written in the contract is true. –– Not that we were expecting anything more from ChatGPT, but this does, interestingly, indicate yet another problem with mockery. I hadn't even picked up on that one earlier. Glad we were able to keep the discussion going to learn more!

But, importantly, we lack necessary information to respond to your question. Perhaps you can clarify the intent here?

[aleksiy123]

You asked for code and I gave you a fairly real world example of where mocking is useful.

My suggestion is for you to provide code how you would test the same handler code and scenario using your methodology.

Show me a test that checks the error handling of quota check. Pretend the quota service is experiencing an outage on the second request you make to it.