ModuleNotFoundError: No module named 'project.appname' when running Django tests

When trying to run my tests using either ./manage.py test or pytest, all of the apps in my Django project fail their tests with ModuleNotFoundError: No module named 'project.appname'. However, when running with ./manage.py test app.tests (if the tests are in a dedicated tests directory), they do progress beyond a Module Not Found error.

I think there is something wrong with my configuration that leads to this error but I have no idea where to poke to try fixing this: I'm not seeing anything that makes PyCharm yell at me when I look at any testing module nor when looking at Settings.py