Thank you for taking the timing and writing this up! I appreciate it a lot and that's why I come back to hackernews! :) Now, your test works and I think I have

Thank you for taking the timing and writing this up! I appreciate it a lot and that's why I come back to hackernews! :) Now, your test works and I think I have to apologize in that I should have understood your approach better and write my answer accordingly. The relevant part of my previous answer: > You WILL end up using a form of "mocking", for example passing the functions B and C as arguments to A and then, under test, don't really pass B and C but different functions that allow you to make assertions in test. That is still mocking. So my point here is that, yes, you are passing functions into the new VerificationEmailController and the ones you pass in are not the same that are being run in production. This is what I call a mock: you replace a dependency that runs in production with one that runs only in the test. That's not to say that your way of testing doesn't work. It's just that it comes with the same conceptual issues (but also benefits) that mocks come with. In particular, 1) if we "misconfigure" the function in our actual production code (i.e. pass the wrong arguments) this won't be covered by the test. Also, 2) we will reimplement certain logic in tests that are necessary to check the actions. Because different actions might still be valid, such as [add5, add5] or [add10] - they come to the same result, but in your assertions you'll need to handle that knowledge, without checking the state, because the state might live in an external system. And 3) Forcing dependencies to be explicit (i.e. function parameters) is neither good nor bad per se, but sometimes it's nicer to have them encapsulated and in this case both classical mocking and your approach stop working. Therefore when it comes to me, I see both classical mocks and your approach as conceptually equal and therefore would call your appraoch mocking too. That's what I wanted to say. I hope that gives you some insight - or maybe you disagree with my 3 points above, then I would be curious why.