That makes no sense at all to me.
If your IPv6 is working you can't go to the site to test it unless you also have working IPv4.
There is absolutely no reason why test-ipv6.com can't have both an A record and an AAAA record.
If your IPv6 is working you can't go to the site to test it unless you also have working IPv4.
There is absolutely no reason why test-ipv6.com can't have both an A record and an AAAA record.
Q: Why is this web site reachable via IPv4 only?
You're right, there are no AAAA records, intentionally. A percentage of users are unable to browse sites that are dual-stack. If the users can't connect, then they can't be told they have a problem. This is a big problem facing content providers today; of which, I work at one for my $dayjob. As such, the main test page requires IPv4 (either native or translated).
At some point, when the percentage of "broken" users has gone significantly down, I'll consider making test-ipv6.com dual-stack..