Comment 4 for bug 1463866

def start_app(path_to_app, window_title):
    p = os.path.normpath(path_to_app)
    if not os.path.exists(p):
        die('cannot find "%s": expected -> %s' % (window_title, p))
    app = App.open(p)
    if not app:
        die('cannot start %s' % window_title)

... then more stuff that waits for the window to appear on the screen ...

   return app