Django test discovery fails

I have a bunch of apps, all are inside a apps folder. I'm adding some tests to my project. It works well, the models / templates / static discovery works super well. Now I would like to add some tests to my projects, so I created a tests.py file inside my app. When I want to run the test (manage.py test) it does not work. I have to specify the name of the app to make it works. I tried with django-nose and I have to same output. I figure out it's because my apps are nested inside a folder but every other django discovery works.