I am not certain that this should be `mkdir`. Depending on the value of `fixture_dir` there might need to be intermediate directories created. It seems more likely to me that this was intended to be `os.makedirs(fixture_dir)` using the `mkdirs` method(see [mkdirs](http://docs.python.org/2/library/os.html#os.makedirs)). I think using `makedirs` here makes more sense.