def test_add_already_added(self):
        prio_set_list = event._PrioritizedSetList()
        obj = object()
        prio_set_list.add(0, obj)

        with pytest.raises(ValueError) as excinfo:
            prio_set_list.add(0, obj)
        excinfo.match(r"has already been added")

        with pytest.raises(ValueError) as excinfo:
            prio_set_list.add(1, obj)
        excinfo.match(r"has already been added")
def list_snapshots(self, params=None):
        """List all the snapshot."""
        url = 'snapshots'
        if params:
                url += '?%s' % urllib.urlencode(params)

        resp, body = self.get(url)
        body = json.loads(body)
        return resp, body['snapshots']