You can test the program with some of the MIDI files that I have produced for my choir Audite. They are found at the homepage of Audite.
Remember that the purpose of these MIDI files is not to give the listener a sublime experience so please bear over with the them. They are only made as a help for the rehearsal where it helps to hear all voices.
Other places with MIDI files for choirs:
You can find a lot of other places containing MIDI files on the web.