Due to the way classes are constructed in Python, and to how tests are grouped in classes when using the unittest module, ordinarily these tests are executed in arbitrary order (sorted by the method name hash in cPython 2.x)
It is not diffcult to imagine situations when we'd like our unittests to run in order (most likely from simpler to more complex tests). Python 3 metaclasses include a feature that unittest could use to ensure ordered execution of tests, if it where coded to do so (the "__prepare__" method in the metaclass can change the assemble-time class dictionary to an ordered dict, and anottate tehe execution ordeer from there).
However, I wanted an implementation that would work in Python 2. So I came up with this "ordered" decorator that can ensure execution order for tests using unittest. It is deliciously hackish, as you can see: the methods are still called in arbitrary order - but what runs is the decorator code, which then takes care of calling the next test in order, regardless of the one unittest thinks is running. :-)
Appart from having to use the functools.wraps decorator (to preserve method names so that unittest actually finds them -- I didn try without it, it might work), the code is rather straightforward once it is written down.
With you, tonight's metapython bit: