'Callables in `defaults` are evaluated if the instance is created.'

def test_callable_defaults(self):

    (obj, created) = Person.objects.get_or_create(first_name='George', defaults={'last_name': 'Harrison', 'birthday': (lambda : date(1943, 2, 25))})
    self.assertTrue(created)
    self.assertEqual(date(1943, 2, 25), obj.birthday)
