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Write Tests First

Метки: python

As I mentioned, one of the problems that I encountered-that most people encounter, it turns out-was submitting to the pressures of publishing and as a result letting tests fall by the wayside. This is easy to do if you forge ahead and write your program code because there’s a little voice that tells you that, after all, you’ve got it working now, and wouldn’t it be more interesting/useful/expedient to just go on and write that other part (we can always go back and write the tests later). As a result, the tests take on less importance, as they often do in a development project.

The answer to this problem, which I first found described in Extreme Programming Explained, is to write the tests before you write the code. This may seem to artificially force testing to the forefront of the development process, but what it actually does is to give testing enough additional value to make it essential. If you write the tests first, you:

  1. Describe what the code is supposed to do, not with some external graphical tool but with code that actually lays the specification down in concrete, verifiable terms.
  2. Provide an example of how the code should be used; again, this is a working, tested example, normally showing all the important method calls, rather than just an academic description of a library.
  3. Provide a way to verify when the code is finished (when all the tests run correctly).

Thus, if you write the tests first then testing becomes a development tool, not just a verification step that can be skipped if you happen to feel comfortable about the code that you just wrote (a comfort, I have found, that is usually wrong).

You can find convincing arguments in Extreme Programming Explained, as “write tests first” is a fundamental principle of XP. If you aren’t convinced you need to adopt any of the changes suggested by XP, note that according to Software Engineering Institute (SEI) studies, nearly 70% of software organizations are stuck in the first two levels of SEI’s scale of sophistication: chaos, and slightly better than chaos. If you change nothing else, add automated testing.