It doesn't seem right to check for 400 after updating policy since your usage above changed. I think it should by default check for 200 and check for other status code based on some optional keyword argument to `_update_policy`. Like:

```python
def _update_policy(self, group_id, policy, upd_args, status=200):
    ...
    self.assertEquals(update_policy_response.status_code, status)
```