add tests for slug function, failing
add tests for slug function, failing

jackwilsdon/beets,SusannaMaria/beets,sampsyo/beets,SusannaMaria/beets,beetbox/beets,SusannaMaria/beets,shamangeorge/beets,ibmibmibm/beets,jackwilsdon/beets,beetbox/beets,shamangeorge/beets,jackwilsdon/beets,ibmibmibm/beets,ibmibmibm/beets,SusannaMaria/beets,ibmibmibm/beets,shamangeorge/beets,jackwilsdon/beets,beetbox/beets,sampsyo/beets,shamangeorge/beets,sampsyo/beets,sampsyo/beets,beetbox/beets