Commit ae43560d45 had added a test with a similar intention. When
the test suite is run on a Fedora Rawhide host, it tests whether the
containers for the two previous stable Fedora releases start or not.
Fedora N-2 reaches End of Life 4 weeks after Fedora N is released [1].
So, testing the containers for Fedora Rawhide and the two previous
stable releases on a Fedora Rawhide host is a decent test of general
backwards compatibility.
However, as seen recently [2], this isn't enough to catch some known
ABI compatibility issues [3,4]. These involve toolbox binaries built
on hosts with newer toolchains that aren't meant to be run against
containers with older runtimes. A targeted test is needed to defend
against these scenarios.
The fedora-toolbox:34 image has glibc-2.33, which is old enough to be
unable to run binaries compiled on Fedora 35 with glibc-2.34 and newer.
[1] https://docs.fedoraproject.org/en-US/releases/
[2] https://github.com/containers/toolbox/pull/1180
[3] Commit 6063eb27b9https://github.com/containers/toolbox/issues/821
[4] Commit 6ad9c63180https://github.com/containers/toolbox/issues/529https://github.com/containers/toolbox/pull/1187