Test cases should use an open-source code license, because someone may want to port or adapt the entire thing as a technical matter.
I don’t use open-source licenses for my games; I don’t think that there’s a real call for ports or adaptations. The originals are playable already.
(Translations are a slightly different issue. I say “If you want to translate one of my games, please contact me first.” This has very rarely happened, but I don’t think I’m the roadblock there – IF translations are high-effort regardless.)
Colin Post has a long-term project to think about this, not in terms of open-sourcing games, but in terms of making them archivable: