The piece of software I'm trying to test is mainly this: https://jazz-soft.net/download/midi-player
but I'm sure many MIDI developers would find such a test suite useful.
Playing XG/GS files would be, of course, a bonus, but there are lots of questions even with GM files,
e.g. can I play type 0/1/2 files? how do I handle SMPTE que points? how I handle UTF8 karaoke text for right-to-left languages?
and many others...
If there is no existing test suite, I can start work to create it, but I don't want to invent another bicycle.