When I run tests I get this error during database initialization:
django.db.migrations.state.InvalidBasesError: Cannot resolve bases for [<ModelState: 'users.GroupProxy'>]
This can happen if you are inheriting models from an app with migrations (e.g. contrib.auth)
proxy = True
verbose_name = Group._meta.verbose_name
verbose_name_plural = Group._meta.verbose_name_plural
After a lot of digging on this the only thing that worked for me was
comment out the offending apps, run migrations, then add them in again.
Just a workaround but hopefully it helps somebody.