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Comment by mike_hearn | Hacker News Reader

I'm curious how you structure your Python to be well testable. I have to admit, my own use of Python has been limited to scripts and (a long time ago) a game engine, not large codebases. So unit testing for those hardly came up.

It seems there's a couple of dependency injection frameworks but they're clones of what's found in Java, right down to the type names. One of them even calls injectable objects beans! (Rhazes)

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Same as you do it in any language: you compose instead of inheriting, you avoid shared state, you generally think about how this thing you're implementing can be tested even as you are implementing it. Test-driven development tends to constrain your interfaces too early but you can get a lot of the same benefits with, let's call it, test-mindful development. That works in any language.

Most of my Python is web. Individual components, same as always - approach with a set API and not too many dependencies, and allow injection via some route if so. I also test web endpoints. One thing I really like is isolating tests that require data -- rather than mocking the database, for example, I'll create an in-memory SQLite DB used while running tests. That way I can test the full stack: a web API, see its results, and check what was changed in the database at the same time, all isolated from the 'real' stack.

I learned to write well testable code when I learned go. It pushes you to pass interfaces instead of direct implementations. There's also no inheritance, just composition. While there's no 1 to 1 translation to Python the concepts are still useful. It can be easier in Python thanks to duck typing.

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