I think ./manage.py test simply does running all the tests trick (in django >= 1.7).
If your organizing tests is about grouping and cherrypicking and you are fan of nose use django nose:
python manage.py test another.test:TestCase.test_method
If you know nose, then you know how to "wildcard" much nicer over all your files.
PS
It is just a better practice. Hope that helps. The answer was borrowed from here: Running a specific test case in Django when your app has a tests directory