Source: 📖 Test Driven Development with Python ch12 p214

Put unit tests in a tests directory

For each Django app created, give it a tests directory to house all the unit tests for that app. This will make it easier to keep all your test files in one place from the beginning. By including an __init__.py file in the tests directory, Django will recognise it and run the tests inside when python manage.py test app_name is called.

You usually want to test each source code file with a different test file in the tests directory, which means that you should end up with test_models.py, test_views.py and test_forms.py