PyCharm throws "AttributeError: 'module' object has no attribute" when running tests for no reason
I had the same problem but my solution was different.
When I tried to run a test from PyCharm, the target path looked like this:

tests.apps.an_app.models.a_model.ATestCase

But since ATest was a class inside a_model.py, the targ path should actually be:

tests.apps.an_app.models.a_model:ATestCase

Changing the target in the test configuration worked.
So, I have a Django-REST Framework project and one day it simply ceased being able to run the tests within PyCharm.
From the command line I can run them both using paver or the manage.py directly.
There was a time when that would happen when we didn't import the class' superclass at the top of the file, but that's not the case.
We have a virtualenv set locally and run the server from a vagrant box. I assured the virtual environment is loaded and that the project's Interpreter is using the afore mentioned virtual env.
No clue on what's the matter.