The shell's test infrastructure currently supports the aliases "latest" and "last-stable" when starting mongodb processes, where those aliases map to the current and previous major mongodb version number, which can be updated in one place when we branch for a new major version. It would be nice to have a similar facility for FCV. Some tests, especially in the multiversion suite, need to explicitly set the FCV to the "previous" version so that can run a mixed-version set, it would be nice to not have to locate and manually update all such tests when the major version changes.