ANN0TEST.DSK is the latest version of the test disk. It only includes 1 MIDI file.
ANN0MIDI.DSK is the previous version that only has the MIDI Format 0 player program, but has 2 additional MIDI files.
If you put ANN0TEST.DSK in drive 1, and ANN0MIDI.DSK in drive 2, rename the volume in drive 1 to something other than /MIDI (ex: /MIDI0). Then the program will look for the midi files in drive 2 and you can play the 3 songs.