code: def _get_config_fname():
      
      directory = _get_vispy_app_dir()
      if directory is None:
          return None
      fname = op.join(directory, 'vispy.json')
      if os.environ.get('_VISPY_CONFIG_TESTING', None) is not None:
          fname = op.join(_TempDir(), 'vispy.json')
      return fname
docs: Helper for the vispy config file