def test_zrank(self):
zset = ZSet()
zset.zadd(a=9, b=7, c=5, d=3, e=1)
self.assertEqual(zset.zrank('a'), 4)
self.assertEqual(zset.zrank('b'), 3)
self.assertEqual(zset.zrank('c'), 2)
self.assertEqual(zset.zrank('d'), 1)
self.assertEqual(zset.zrank('e'), 0)
def test_zrank_not_in_set(self):
zset = ZSet()
self.assertEqual(zset.zrank('a'), None)
zset.zadd(a=9, b=7, c=5, d=3, e=1)
self.assertEqual(zset.zrank('z'), None)
