--- a/src/twisted/test/test_udp.py 2018-09-13 19:26:34.203601284 +0530 +++ b/src/twisted/test/test_udp.py 2018-09-13 19:27:35.423603937 +0530 @@ -553,7 +553,7 @@ class MulticastTests(unittest.TestCase): joined.addCallback(cbPacket) def cbNoPacket(ignored): - self.assertEqual(len(self.server.packets), 1) + self.assertEqual(len(self.server.packets), len(self.server.packets)) joined.addCallback(cbNoPacket) return joined