'Ensure that inheritance is disabled by default on simple
classes and that _cls will not be used.'

def test_allow_inheritance(self):

    class Animal(Document, ):
        name = StringField()
    with self.assertRaises(ValueError):
        class Dog(Animal, ):
            pass
    dog = Animal(name='dog').save()
    self.assertEqual(dog.to_mongo().keys(), ['_id', 'name'])
    collection = self.db[Animal._get_collection_name()]
    obj = collection.find_one()
    self.assertFalse(('_cls' in obj))
