human
Solve the following python programming problem given the following code:
@ mock.patch ('nova.db.instance_tag_delete') 
def test_delete_non_existing_tag(self, mock_db_delete_inst_tags) : 
    def fake_db_delete_tag(context, instance_uuid, tag) : 
        self.assertEqual (UUID, instance_uuid) 
        self.assertEqual (TAG1, tag) 
        raise exception.InstanceTagNotFound (instance_id = instance_uuid, tag = tag) 
mock_db_delete_inst_tags.side_effect = <MASK> 
    req = self._get_request (('/v2/fake/servers/%s/tags/%s' % (UUID, TAG1)), 'DELETE') 
    self.assertRaises (exc.HTTPNotFound, self.controller.delete, req, UUID, TAG1) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: req, mock_db_delete_inst_tags, self
assistant
#Here is a proper replacement for <MASK>.
def fake_db_delete_tag(