Screaming Penguin - Source Does Matter

Point taken. (Hmm, I hate to engage in yet another static vs dynamic argument since this has already been done to the death in many places, but here it goes...) I agree maintaining tests is a tax, but I also think that declaring type information in your code is another kind of tax. They are not the same, and they have different properties. Tests are more powerful than static type checking, I think it's agreed that even if you have static typing, you still need written tests. Static type declarations takes less effort to maintain than tests. I agree with you that type declarations can serve as good documentation for APIs. In practice, learning APIs for ruby or python usually involve reading documentation(there IS documentation) and trying things out in the interactive shell(where you can also do introspection of objects). I read Cedric's: "looking at the sources of the tests(does anyone ever do that?)" argument. That front is improving with Behavior Driven Development, which is making tests more declarative and readable and has a lot of momentum now.

Another point I want to make is that if you write tests well, you write them to test only where it counts and no more. This makes refactoring easier because you can change around the things that you don't care about as much - or more volatile and not covered by tests as rigidly - and still not break a lot of tests, which at that point you have less tests to maintain(in terms of having to fix them). Where as, with static typing, type declaration is alway mandatory(in most languages anyway). If you consider every type declaration a tiny test, you basically have to write many extra tiny test for every time you create a new function(actually, to be precise, one for each input and output parameter). Therefore, the more functions you have, the more "tiny tests" you'll have, and you will have to maintain them, there's no way to opt out.