'Execute the fetch_art coroutine for the task and return the
album\'s resulting artpath. ``should_exist`` specifies whether to
assert that art path was set (to the correct value) or or that
the path was not set.'

def _fetch_art(self, should_exist):

    self.plugin.fetch_art(self.session, self.task)
    self.plugin.assign_art(self.session, self.task)
    artpath = self.lib.albums()[0].artpath
    if should_exist:
        self.assertEqual(artpath, os.path.join(os.path.dirname(self.i.path), 'cover.jpg'))
        self.assertExists(artpath)
    else:
        self.assertEqual(artpath, None)
    return artpath
