def METHOD_NAME(tor_path = None):
  """
  Provides the version of tor we're testing against.
  :param str tor_path: location of tor executable to cehck the version of
  :returns: :class:`~stem.version.Version` of tor invoked by our integration
    tests
  """
  global TOR_VERSION
  if TOR_VERSION is None or tor_path:
    TOR_VERSION = stem.version.get_system_tor_version(tor_path)
  return TOR_VERSION