Testsuite fails on IPv6-only hosts

[SnarkBoojum]

The testsuite should detect it runs on a host with only IPv6 and hence disable automatically IPv4-dependent tests.

[agronholm]

Never in my career have I come across a host that does not support IPv4. I've never seen any other project account for this either.

[SnarkBoojum]

Well, unless this bug report misinterpreted the error log, you now have your first time.

[agronholm]

To be perfectly honest, I'm not sure I know how to set up such an environment. Even when running a Docker container with --network none, it can still bind to 127.0.0.1. Do I need to run a full VM for this? Can I somehow test this with GitHub Actions?

Anyhow, I've set up a branch (ipv6only) where IPv4 using tests should be skipped if it's not available. Would you mind testing against it?

[SnarkBoojum]

I haven't tested your patch yet, but I asked around how to do it and was pointed to a different diagnosis for the issue.

[agronholm]

I also saw that the container failed to resolve localhost when networking was disabled, and this patch ensures that those tests are skipped in that situation.