old_contents: from django.db.models.base import ModelBase
  from django.db.models.loading import cache
  
  
  class AbstractModelMixin(object):
      """
      Mixin class for tests of model mixins. To use, subclass and specify
      the mixin class variable. A model using the mixin will be made
      available in self.model.
  
      From http://michael.mior.ca/2012/01/14/unit-testing-django-model-mixins/
      via http://stackoverflow.com/a/9678200/400691, modified as we don't need an
      object in the database.
      """
      def setUp(self):
          # Create a dummy model which extends the mixin
          self._model_name = '__TestModel__' + self.mixin.__name__
          self.model = ModelBase(
              self._model_name,
              (self.mixin,),
              {'__module__': self.mixin.__module__},
          )
  
      def tearDown(self):
          # Ensure we don't leave our test model in the model cache
          articles = cache.app_models['articles']
          del articles[self._model_name.lower()]
  
new_contents: from django.db.models.base import ModelBase
  
  
  class AbstractModelMixin(object):
      """
      Mixin class for tests of model mixins. To use, subclass and specify
      the mixin class variable. A model using the mixin will be made
      available in self.model.
  
      From http://michael.mior.ca/2012/01/14/unit-testing-django-model-mixins/
      via http://stackoverflow.com/a/9678200/400691, modified as we don't need an
      object in the database.
      """
      def setUp(self):
          # Create a dummy model which extends the mixin
          self._model_name = '__TestModel__' + self.mixin.__name__
          self.model = ModelBase(
              self._model_name,
              (self.mixin,),
              {'__module__': self.mixin.__module__},
          )
  
subject: Remove app-specific tearDown logic