Django: Best way to unit-test an abstract model

I need to write some unit tests for an abstract base model, that provides some basic functionality that should be used by other apps. It it would be necessary to define a model that inherits from it just for testing purposes; are there any elegant/simple ways to define that model just for testing?

I have seen some "hacks" that make this possible, but never seen an "official" way in the django documentation or in other similar places.