Starting out with unittests

It’s a big shame because your very first experience of unittesting is unittest.main and your next experience is this brick wall of suck and you think… I’m just not going to use it.


Andrew and I have had Jonathan Lange to visit this week while he awaits home Internet, which means there’s been a lot of talk about unit testing.

Coincidently, today I am at the very beginning of a small-ish Python project, one just large enough that I’d like to make sure it’s fairly correct from the beginning, meaning I’d like to make sure it has automated tests, a sensible module layout and that kind of thing. It’s small enough that I bet I could get it working quickly enough without automated tests… and therein lies the trap. In order to do the right thing when starting a scratch project, doing the right thing needs to be either really really easy, or really easy to correct if it was skipped at the junkcode stage of the project.

Consider various aspects of the project. I haven’t worried too much about correct module naming, because at least with Bazaar renaming directories will be easy to do later. But I am trying to do unit testing from the very beginning because adding good testing to an existing codebase of much over 200 lines converges on impossible pretty quickly. And since I create new files in Python the way some other people create functions and some other other people create new lines, I separate my test modules early which results in this brick wall of suck:

 import unittest  tests = [ # list of strings containing test module names ]  def my_import(name): # No love to mod = __import__(name) components = name.split('.') for comp in components[1:]: mod = getattr(mod, comp) return mod  def runAll(): runner = unittest.TextTestRunner() suite = unittest.TestSuite() for testmodulename in tests: testmodule = my_import(testmodulename) print testmodule loader = unittest.TestLoader() suite.addTests(loader.loadTestsFromModule(testmodule)) result = 

That is, unittest does not do test discovery, you have to tell it where to find all the test modules, and you run slap-bang into Python’s tedious programmatic interface to its own import mechanisms.

So, unit testing in Python: hard to get right later, but not easy enough to get right at the beginning. (Consider: the code above is currently about three quarters of the codebase in question.) I will watch Jonathan’s pyunit3k with interest. (For my PhD I use Twisted’s trial test runner, but I am not willing to introduce a dependency on Twisted for this project purely for a better test runner.)

In general, it would be excellent if some firm and right person was to write a guide to best practices for Python projects, with regard to starting a project so that it is easy to test, easy to collaborate on, easy to install and (and I think this is somewhat missing too) easy for the distributions to package. And that all these steps be so trivial that they can be carried out at the beginning of almost every project.