How to use the ubiquerg.is_command_callable function in ubiquerg

def get_dir_digest(path, pm=None):
    """
    Generate a MD5 digest that reflects just the contents of the files in the selected directory.

    :param str path: path to the directory to digest
    :param pypiper.PipelineManager pm: a pipeline object, optional. The subprocess module will be used if not provided
    :return str: a digest, e.g. a3c46f201a3ce7831d85cf4a125aa334
    """
    if not is_command_callable("md5sum"):
        raise OSError("md5sum command line tool is required for asset digest calculation. \n"
                      "Install and try again, e.g on macOS: 'brew install md5sha1sum'")
    cmd = "cd {}; find . -type f -not -path './" + BUILD_STATS_DIR + \
          "*' -exec md5sum {{}} \; | sort -k 2 | awk '{{print $1}}' | md5sum"
    if isinstance(pm, pypiper.PipelineManager):
        x = pm.checkprint(cmd.format(path))
    else:
        try:
            from subprocess import check_output
            x = check_output(cmd.format(path), shell=True).decode("utf-8")
        except Exception as e:
            _LOGGER.warning("{}: could not calculate digest for '{}'".format(e.__class__.__name__, path))
            return
    return str(sub(r'\W+', '', x))  # strips non-alphanumeric