We had a couple of areas where we made some bad assumptions about static

media. These were specific to unit tests.
First, tests/settings.py build absolute paths relative to the current

working directory, assuming that directory would be tests. This won't

be a safe assumption when using pytest. Instead, we now build a path

relative to the tests/settings.py file.
We also had a test that deleted and rebuild some static media

directories. It assumed all parent directories for the static media path

existed, but this wasn't safe either. We now use os.makedirs() to

construct all missing parents.

Unit tests pass with the old test runner and the new pytest one in

all supported versions of Python.