Question

Are you doing test first anyway? Or in some cases you are doing some coding and then writing your tests to make sure code works? As for me I prefer to create a class. Sure, during class creation I think about its interface and how to test the class. But I dont write testing code first. Do you write it first? Do you think you should always write test code first?

Answer 1

I’m not a purist in this matter (TDD involves more than just writing the tests first, it’s also about initially writing very minimal, “hard coded” tests and refactoring them a lot — see The Book by The Master himself).

I tend to test-first when I’m doing incremental development to add a feature to an existing module, and I insist on test-first when the incremental development I’m doing is to fix a bug (in the latter case I absolutely want a unit-test AND an integration-test that both reproduce the bug, before I fix the code that caused the bug).

I tend to be laxer when I’m doing “greenfield” development, especially if that’s of an exploratory, “let’s see what we can do here that’s useful”, nature — which does happen, e.g. in data mining and the like — you have a somewhat vague idea that there might be a useful signal buried in the data, some hypothesis about its possible nature and smart ways to [maybe] extract it — the tests won’t help until the exploration has progressed quite a bit.

And, once I start feeling happy with what I’ve got, and thus start writing tests, I don’t necessarily have to redo the “exploratory” code from scratch (as I keep it clean and usable as I go, not too hard to do especially in Python, but also in R and other flexible languages).