def test_cachedResultExpires(self):
        """
        Once the TTL has been exceeded, the result is removed from the cache.
        """
        r = ([dns.RRHeader(b"example.com", dns.A, dns.IN, 60,
                           dns.Record_A("127.0.0.1", 60))],
             [dns.RRHeader(b"example.com", dns.A, dns.IN, 50,
                           dns.Record_A("127.0.0.1", 50))],
             [dns.RRHeader(b"example.com", dns.A, dns.IN, 40,
                           dns.Record_A("127.0.0.1", 40))])

        clock = task.Clock()

        c = cache.CacheResolver(reactor=clock)
        query = dns.Query(name=b"example.com", type=dns.A, cls=dns.IN)
        c.cacheResult(query, r)

        clock.advance(40)

        self.assertNotIn(query, c.cache)

        return self.assertFailure(
            c.lookupAddress(b"example.com"), dns.DomainError)

        Once the TTL has been exceeded, the result is removed from the cache.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_cache.py