'The default implementation of __str__ and __repr__ should return
instances of str.'

@isolate_apps('str')
def test_defaults(self):

    class Default(models.Model, ):
        pass
    obj = Default()
    self.assertIsInstance(obj.__str__(), str)
    self.assertIsInstance(obj.__repr__(), str)
    self.assertEqual(str(obj), 'Default    object    (None)')
    self.assertEqual(repr(obj), '<Default:    Default    object    (None)>')
    obj2 = Default(pk=100)
    self.assertEqual(str(obj2), 'Default    object    (100)')
    self.assertEqual(repr(obj2), '<Default:    Default    object    (100)>')
