old_contents: import datetime
  
  from django.db import models
  from nose.tools import nottest
  
  
  class Base(models.Model):
      class Meta:
          abstract = True
      char_value = models.CharField(max_length=100, default='')
      int_value = models.IntegerField(default=0)
      date_value = models.DateField(default=datetime.date.today)
      datetime_value = models.DateTimeField(default=datetime.datetime.now)
  
  
  @nottest
  class TestObj(Base):
      parent = models.ForeignKey('self', related_name='children', null=True)
      m2ms = models.ManyToManyField(
          'testapp.M2MModel', related_name='test_objs')
  
      @property
      def some_property(self):
          return {'x': 'y'}
  
      def __repr__(self):
          return "<TestObj: %d>" % self.id
  
  
  class M2MModel(Base):
      pass
  
  
  class OneToOneModel(Base):
      test_obj = models.OneToOneField(
          TestObj, null=True)
  
  
  class CustomRelatedNameOneToOneModel(Base):
      test_obj = models.OneToOneField(
          TestObj, related_name='custom_one_to_one', null=True)
  
  
  class ForeignKeyModel(Base):
      test_obj = models.ForeignKey(TestObj, null=True)
  
new_contents: import datetime
  
  from django.db import models
  from nose.tools import nottest
  
  
  class Base(models.Model):
      class Meta:
          abstract = True
      char_value = models.CharField(max_length=100, default='')
      int_value = models.IntegerField(default=0)
      date_value = models.DateField(default=datetime.date.today)
      datetime_value = models.DateTimeField(default=datetime.datetime.now)
  
  
  @nottest
  class TestObj(Base):
      parent = models.ForeignKey('self', related_name='children', null=True, on_delete=models.CASCADE)
      m2ms = models.ManyToManyField(
          'testapp.M2MModel', related_name='test_objs')
  
      @property
      def some_property(self):
          return {'x': 'y'}
  
      def __repr__(self):
          return "<TestObj: %d>" % self.id
  
  
  class M2MModel(Base):
      pass
  
  
  class OneToOneModel(Base):
      test_obj = models.OneToOneField(
          TestObj, null=True, on_delete=models.CASCADE)
  
  
  class CustomRelatedNameOneToOneModel(Base):
      test_obj = models.OneToOneField(
          TestObj, related_name='custom_one_to_one', null=True, on_delete=models.CASCADE)
  
  
  class ForeignKeyModel(Base):
      test_obj = models.ForeignKey(TestObj, null=True, on_delete=models.CASCADE)
  
subject: Add required `on_delete` kwarg.