short silent tracks can be generated with audacity. Select the `silence` option
from the `generate menu`

To add a new test file make a copy of `empty.mp3` and name it appropriately.
Then you can prepare the id3 tags using `id3v2`. Please also write the commands
in here used with `id3v2`

artist.mp3
    id3v2 --artist "Test Artist" artist.mp3

TOAL_TPE2.mp3
    id3v2 --artist "TITLE2" --TPE2 "TITLE" --TOAL "ARTIST" TOAL_TPE2.mp3

cover-test.aiff
cover-test.flac
cover-test.mp3
cover-test.ogg
cover-test.wav
    this is a exception because id3v2 can't set a cover. This was created using easytag