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)

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).

It allows you to mock the whole universe so it becomes a hammer instead of nicely designed functions, interfaces.

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’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).