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> if you don't think of the possibility that a library call might return null then you wouldn't write a test for it either No, I don't think so. I'll write a

> if you don't think of the possibility that a library call might return null then you wouldn't write a test for it either No, I don't think so. I'll write a test that uses the library. If the library returns null when I don't expect it, it'll go into my code an cause an exception to tbe thrown. I'm not deliberately testing for nulls, I'm testing generally that my code does what I think it does.

lmm 10y ago
> No, I don't think so. I'll write a test that uses the library. If the library returns null when I don't expect it, it'll go into my code an cause an exception to tbe thrown. I'm not deliberately testing for nulls, I'm testing generally that my code does what I think it does. The kind of library function that returns null doesn't usually return it on the "happy path", it usually returns null for some weird condition you haven't thought of. I mean, if it's a function that returns null often or that you'd expect to sometimes return null, you'll wrap up the return value in an option straight away even without having written a test. The kind of library function that causes you to get exceptions in production is the kind that returns null in some weird corner case - but unless you think of the weird corner case, you wouldn't hit it in a test either. If I was using a library with some complex stateful interface I might write tests for the interaction with that (I'd probably put a facade on it, keeping it separate from the business logic, and the facade would have unit tests) - but I'd try to avoid using such a library. And I'll always have a few high-level end-to-end tests (not really "unit" tests) as a basic "does it work at all", because that kind of mistake is easy to make. But the bread-and-butter unit tests that I wrote when I worked in Python just don't seem valuable or necessary.
- winstonewert 10y ago
  I think you are assuming saner code then I'm used to. Honestly, I can't say how it would work if I was using a java code base that consistently applied these kinds of ideas. You may be right, but at this point I have hard time believing.
  - lmm 10y ago
    I've worked on some bad codebases. You can convert a little bit at a time, treating the remainder of the codebase as a large library with a poorly factored interface. You absolutely will need unit test coverage at the boundary, which will probably exist for several years.

lmm 10y ago

> No, I don't think so. I'll write a test that uses the library. If the library returns null when I don't expect it, it'll go into my code an cause an exception to tbe thrown. I'm not deliberately testing for nulls, I'm testing generally that my code does what I think it does. The kind of library function that returns null doesn't usually return it on the "happy path", it usually returns null for some weird condition you haven't thought of. I mean, if it's a function that returns null often or that you'd expect to sometimes return null, you'll wrap up the return value in an option straight away even without having written a test. The kind of library function that causes you to get exceptions in production is the kind that returns null in some weird corner case - but unless you think of the weird corner case, you wouldn't hit it in a test either. If I was using a library with some complex stateful interface I might write tests for the interaction with that (I'd probably put a facade on it, keeping it separate from the business logic, and the facade would have unit tests) - but I'd try to avoid using such a library. And I'll always have a few high-level end-to-end tests (not really "unit" tests) as a basic "does it work at all", because that kind of mistake is easy to make. But the bread-and-butter unit tests that I wrote when I worked in Python just don't seem valuable or necessary.

winstonewert 10y ago
I think you are assuming saner code then I'm used to. Honestly, I can't say how it would work if I was using a java code base that consistently applied these kinds of ideas. You may be right, but at this point I have hard time believing.
- lmm 10y ago
  I've worked on some bad codebases. You can convert a little bit at a time, treating the remainder of the codebase as a large library with a poorly factored interface. You absolutely will need unit test coverage at the boundary, which will probably exist for several years.