test-ipv6.com is intentionally IPv4-only, because otherwise people with broken IPv6 wouldn't be able to run the test. It's covered in the FAQ:<p><a href="http://test-ipv6.com/faq.html" rel="nofollow">http://test-ipv6.com/faq.html</a><p>However, the prevalence of IPv6 brokenness has declined a bit since most browsers started doing Happy Eyeballs.