Could the same thing be achieved by subclassing your base test class and then overriding setUp to inject the correct data for that combination? I'm pretty sure I'm oversimplifying, but I'm really interested in your method.

In Django, when we add a new field type, you need to remember to test all the integrations (admin, forms, migrations, etc) and that's not always done correctly. It'd be great if there were some easier method than just subclassing a template test class and implementing all tests from the ground up.