test: Split up playlist test helper class
test: Split up playlist test helper class

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