我想在django中对www.example.com进行单元测试models.py。我不知道如何对函数natural_key（）进行单元测试

class User(AbstractBaseUser, PermissionsMixin):
    email = models.EmailField(_('email address'), unique=True)
    username = models.CharField(max_length=10, default="default", null=True, blank=True)

    @property
    def natural_key(self):
        return (self.email, self.username)

我试过了

self.user1 = User.objects.create(
     email="user@email.com"
     username="username1")

def test_natural_key_is_created(self):
   self.assertEquals(self.user1.natural_key, "user@email.com", "username1")

但是我的单元测试失败了