Run ruby/spec in TravisCI on older versions of MRI to make sure the specs keep working with older supported versions
ruby/spec is a single codebase supporting the latest minor versions of all supported MRI versions.
So currently, that's 2.3.7, 2.4.4, 2.5.1 and trunk.
I want to make MRI developers aware that ruby/spec must keep working with older (supported) versions,
and that version guards (
ruby_version_is) are necessary for features which differ by version.
I added a note about that in spec/README.md in r64410.
To help awareness about that, I want to run specs on 2.3.7 (the oldest version) in ruby/ruby's TravisCI to catch missing version guards early.
Otherwise, I have, alone, to add all missing version guards when merging specs monthly, which is a fair bit of work.
I tried it on my ruby/ruby fork in TravisCI and it adds around 1 minute, which seems reasonable (AppVeyor takes much longer anyway):
I plan to merge this soon, after making sure it works with latest trunk.