Appropriate placement for my testcases belonging to a non-app in Django

I have built my website in Django. And like any other django project I have got apps inside the project root directory and some special folders like(extensions a.k.a custom django command extensions). With an app, we dont have any problem with having testcases. "tests.py" inside the app directory will be the solution. But for a special folder(which is not an app or which doesn't have a models.py) where do I place the testcases. I tried placing the tests.py inside the extensions directory and it said the directory is not a model and unable to run the tests. HOw do I solve this? How can I have a proper placement of testcases related to non-apps?