def test_empty_list(self):
        self.assertIs(
            None, _latest_common_snapshot([Snapshot(name=b"a")], []))
grouper(3, 'abcdefg', 'x') --> ('a','b','c'), ('d','e','f'),
dataset/ETHPy150Open ClusterHQ/flocker/flocker/volume/test/test_filesystems_zfs.py/LatestCommonSnapshotTests.test_empty_list--crossover with--dataset/ETHPy150Open lsbardel/python-stdnet/stdnet/utils/__init__.py/grouper