This was first observed in review for #1709. The issue was resolved for py3 tests at the time by updating the test container to pull in the newer libmodulemd2. When #1709 was merged, py2 tests were still failing (independent of the pr), but an update to epel for a newer libmodulemd2 was pending.

That update has landed, and epel has even moved on to libmodulemd2-2.13.0 since, but the unit tests for py2 are still failing, even with a freshly rebuilt container image.