You've just built a calculator, and now you want to test it. Well, you have to push buttons on a calculator, so you build a robotic hand. And that hand needs a power source and some intelligence. And you need to photograph and OCR the result from the calculator screen.
This is kinda how we build software right? A little bit of "our logic" (calculation), represented as objects/actors/modules which "do things", but intermingled with million-LoC dependencies like databases and web servers.
After a while it gets frustrating setting up the robot hand and OCR equipment for each test case. Maybe it's just easier to test manually, or skip testing entirely.
At this point you can have an epiphany, and realise you only care about the numbers going in and out of the calculator, not the button pushes and pixels.
Mockito swoops in and prevents you from having that epiphany, by making it easier to keep doing things the stupid way.
Instead isolating the calculation from any IO, you can now write things like:
when(finger.pushbutton(1)).then(calculator.setState(1))
when(calculator.setAnswer(3)).then(camera.setOcr(3))
(I've mostly worked in Java, but it seems like other languages typically don't let you intercept calls and responses this way)
I’ll answer: Nothing specific to Mockito, it happens in every language. Tests “solidify” code which makes refactoring hard. And yet, after refactoring, one can be happy to have tests to check whether there is any regression.
Testing is hard. I’ve tried with AI today: No, it is still not capable of handling that kind of (straightforward) task (Using Claude).
They also encourage/enable code that is less testable. If you use mockito to get your fake responses/assertions where you need them, you don't have to think about your class's dependencies to make your code testable and therefore better decomposed. I don't even do TDD, but I still find that thinking about how I'd test a class guides me toward better-factored code.
One alternative to make code with typing styles in the Java way (as opposed to the Typescript or Go way) is to have a whole lot of custom interfaces and then you end up with a whole bunch of:
doTheThing(foo: Fooable) { ... }
when there's really only one Foo implementation in prod. It leads to (what feels like, to me) more code obfuscation in large projects, than the benefits that come out, at least for me.
So Mockito and friends are a nice alternative to that.
That is just my experience and opinion though, and there are definitely more valid or equally valid alternatives.
I don't think we have to choose. Naturally finding the "right division of labor" is as infinite as finding the "right level of abstraction", but I think the ideal situation is to strive toward code that is easy to test without having to introduce a lot of mocks or without infinite layers of abstraction.
IMO Mockito is fine, the problem I’ve encountered is people taking the easy way out and trying to test something that needs a real integration test with a convoluted series of mocks.
I agree. I mostly only use mocks for external service dependencies (apart from primary application database), or library features that are very problematic to use in test. A lot of code simply should not be unit tested - if an integration test can cover the same paths its far better in the long run. Performance can become an issue but it is easier to deal with that than to spend so much time maintaining and debugging mock constructs.
I’ve been on projects where mocking _literally made the project less reliable_ because people ended up “testing” against mocks that didn’t accurately reflect the behavior of the real APIs.
It left us with functionality that wasn’t actually tested and resulted in real bugs and regressions that shipped.
Mocking is one of these weird programmer pop-culture memetic viruses that spread in the early 2000s and achieved complete victory in the 2010s, like Agile and OOP, and now there are entire generations of devs who it’s not that they’re making a bad or a poorly argued choice, it’s that they literally don’t even know there are other ways of thinking about these problems because these ideas have sucked all the oxygen out of the room.
I think there's room to argue "Agile" is a popular bastardisation of what's meant by "agile software development", and with "OOP" we got the lame Java interpretation rather than the sophisticated Smalltalk interpretation. -- Or I might think that these ideas aren't that good if their poor imitations win out over the "proper" ideas.
With mocking.. I'm willing to be curious that there's some good/effective way of doing it. But the idea of "you're just testing that the compiler works" comes to mind.
For OOP, I'd say the issue isn't so much that it's not useful (it is very useful), but rather that it was treated as "common sense, the only way to do it".
Sometimes the right tool for the job is objects, sometimes it's functional, sometimes you do want encapsulation but it's better as structs and using composition over inheritance. When everything looks like a `class Hammer extends Tool`…
Agreed - I like your phrasing of it. There are some good ideas in OOP. I don't know that I'd go as far as to credit OOP for those ideas, but things like polymorphism and encapsulation can be very useful. What I objected to was, as you said, OOP became "the only way to do it". It became a dogma. I was very happy when functional programming started to break through and show that there were other ways that were not only viable, but often better.
Mocking and integration tests are not mutually exclusive. I often use mocks in my integration tests. Some things can be integration tested, some things can't. Sone things you just need to mock.
People using it wrong. It definitely should not be that popular. 95% of times when I see it I consider it a tech debt.
You should be using it in rare cases when you want to verify very complex code that needs to be working with strict requirements (like calling order is specified, or some calls cannot be made during execution of the method).
Usually it is used for pointless unit tests of simple intermediary layers to test if call is delegated correctly to deeper layer. Those tests usually have negative value (they test very little but make any modification much harder).
