Code of the test with a comment on the line which fails:

    def test_control_and_wait(self):
        client, server = self._connected_pair()

        ep = select.epoll(16)
        ep.register(server.fileno(),
                    select.EPOLLIN | select.EPOLLOUT | select.EPOLLET)
        ep.register(client.fileno(),
                    select.EPOLLIN | select.EPOLLOUT | select.EPOLLET)

        now = time.monotonic()
        events = ep.poll(1, 4)
        then = time.monotonic()
        self.assertFalse(then - now > 0.1, then - now)

        events.sort()
        expected = [(client.fileno(), select.EPOLLOUT),
                    (server.fileno(), select.EPOLLOUT)]
        expected.sort()

        self.assertEqual(events, expected)

        events = ep.poll(timeout=2.1, maxevents=4)
        self.assertFalse(events)

        client.send(b"Hello!")
        server.send(b"world!!!")

        now = time.monotonic()
        events = ep.poll(1, 4)
        then = time.monotonic()
        self.assertFalse(then - now > 0.01)

        events.sort()
        expected = [(client.fileno(), select.EPOLLIN | select.EPOLLOUT),
                    (server.fileno(), select.EPOLLIN | select.EPOLLOUT)]
        expected.sort()

        self.assertEqual(events, expected) # <====== FAIL HERE

        ep.unregister(client.fileno())
        ep.modify(server.fileno(), select.EPOLLOUT)
        now = time.monotonic()
        events = ep.poll(1, 4)
        then = time.monotonic()
        self.assertFalse(then - now > 0.01)

        expected = [(server.fileno(), select.EPOLLOUT)]
        self.assertEqual(events, expected)