How to use the rospkg.get_ros_root function in rospkg

def setUp(self):
        if 'ROSDEP_DEBUG' in os.environ:
            del os.environ['ROSDEP_DEBUG']
        self.old_rr = rospkg.get_ros_root()
        self.old_rpp = rospkg.get_ros_package_path()
        self.old_app = os.getenv(AMENT_PREFIX_PATH_ENV_VAR, None)
        if 'ROS_ROOT' in os.environ:
            del os.environ['ROS_ROOT']
        os.environ['ROS_PACKAGE_PATH'] = os.path.join(get_test_tree_dir())
        os.environ[AMENT_PREFIX_PATH_ENV_VAR] = os.path.join(get_test_tree_dir(), 'ament')
        if 'ROS_PYTHON_VERSION' not in os.environ:
            # avoid `test_check` failure due to warning on stderr
            os.environ['ROS_PYTHON_VERSION'] = sys.version[0]

def get_ros_root(required=False, env=None):
    """
    Get the value of ROS_ROOT.
    @param env: override environment dictionary
    @type  env: dict
    @param required: if True, fails with ROSException
    @return: Value of ROS_ROOT environment
    @rtype: str
    @raise ROSException: if require is True and ROS_ROOT is not set
    """
    if env is None:
        env = os.environ
    ros_root = rospkg.get_ros_root(env)
    if required and not ros_root:
        raise rospy.exceptions.ROSException('%s is not set'%rospkg.environment.ROS_ROOT)
    return ros_root

def rle_wrapper(fn):
    """
    Wrap lower-level exceptions in RLException class
    :returns:: function wrapper that throws an RLException if the
        wrapped function throws an Exception, ``fn``
    """    
    def wrapped_fn(*args):
        try:
            return fn(*args)
        except Exception as e:
            # we specifically catch RLExceptions and print their messages differently
            raise RLException("ERROR: %s"%e)
    return wrapped_fn
        
get_ros_root         = rospkg.get_ros_root
get_master_uri_env   = rle_wrapper(rosgraph.get_master_uri) 
get_ros_package_path = rospkg.get_ros_package_path

def remap_localhost_uri(uri, force_localhost=False):
    """
    Resolve localhost addresses to an IP address so that
    :param uri: XML-RPC URI, ``str``
    :param force_localhost: if True, URI is mapped onto the local machine no matter what, ``bool``
    """
    hostname, port = rosgraph.network.parse_http_host_and_port(uri)
    if force_localhost or hostname == 'localhost':
        return rosgraph.network.create_local_xmlrpc_uri(port)
    else:
        return uri

##################################################################

logfile_dir = os.path.dirname(log_filename)
    if not os.path.exists(logfile_dir):
        try:
            makedirs_with_parent_perms(logfile_dir)
        except OSError:
            # cannot print to screen because command-line tools with output use this
            sys.stderr.write("WARNING: cannot create log directory [%s]. Please set %s to a writable location.\n"%(logfile_dir, ROS_LOG_DIR))
            return None
    elif os.path.isfile(logfile_dir):
        raise LoggingException("Cannot save log files: file [%s] is in the way"%logfile_dir)

    if 'ROS_PYTHON_LOG_CONFIG_FILE' in os.environ:
        config_file = os.environ['ROS_PYTHON_LOG_CONFIG_FILE']
    else:
        config_file = os.path.join(get_ros_root(env=env), 'config', 'python_logging.conf')

    if not os.path.isfile(config_file):
        # logging is considered soft-fail
        sys.stderr.write("WARNING: cannot load logging configuration file, logging is disabled\n")
        return log_filename
    
    # pass in log_filename as argument to pylogging.conf
    os.environ['ROS_LOG_FILENAME'] = log_filename
    # #3625: disabling_existing_loggers=False
    logging.config.fileConfig(config_file, disable_existing_loggers=False)
    return log_filename

def get_cwd(cwd, binary=''):
    result = ''
    if cwd == 'node':
        result = os.path.dirname(binary)
    elif cwd == 'cwd':
        result = os.getcwd()
    elif cwd == 'ros-root':
        result = rospkg.get_ros_root()
    else:
        result = rospkg.get_ros_home()
    if not os.path.exists(result):
        try:
            os.makedirs(result)
        except OSError:
            # exist_ok=True
            pass
    return result