BPD tests: improve helpers
BPD tests: improve helpers

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