Only include real models_modules.
Review Request #8719 — Created Feb. 6, 2017 and submitted
The new implementation to get a list of all the models modules wasn't filtering
out apps that didn't have any models, which meant that some of the entries were
None. This then failed when trying to get fixture directories for each of the
tests.
Ran reviewboard unit tests.
Tool: Pyflakes Processed Files: djblets/testing/testcases.py Tool: PEP8 Style Checker Processed Files: djblets/testing/testcases.py