@lightsofapollo @gaye 
I would prefer it if this function could be part of the marionette lib or a more general API than this specific test suite. Also I have no idea how many plattforms we will test this on what the correct directories are and if they differ with OS versions. Any suggestion on how this could be made cross platform? 

Additionally, this should probably be part of JS marionette runner API. I guess other apps like the music app will need something similiar. Maybe we should consider moving the whole getMediaDir() method to a marionette utility API. How can I help doing this?