tries to find current git tag

    Notes:
        git_command exposed for testing null case

    Args:
        default_version (str): what version to make
        git_command (:obj:`list`): subprocess command

    Retruns:
        str: latest version found, or default

    Warns:
        exceptions.ProsperDefaultVersionWarning: git version not found

def _read_git_tags(
        default_version=DEFAULT_VERSION,
        git_command=('git', 'tag'),
):
    """tries to find current git tag

    Notes:
        git_command exposed for testing null case

    Args:
        default_version (str): what version to make
        git_command (:obj:`list`): subprocess command

    Retruns:
        str: latest version found, or default

    Warns:
        exceptions.ProsperDefaultVersionWarning: git version not found

    """
    try:
        current_tags = check_output(git_command).splitlines()
    except Exception:  # pragma: no cover
        raise

    if not current_tags[0]:
        warnings.warn(
            'Unable to resolve current version',
            exceptions.ProsperDefaultVersionWarning)
        return default_version

    latest_version = semantic_version.Version(default_version)
    for tag in current_tags:
        tag_str = decode(tag, 'utf-8').replace('v', '')
        try:
            tag_ver = semantic_version.Version(tag_str)
        except Exception:  # pragma: no cover
            continue  # invalid tags ok, but no release

        if tag_ver > latest_version:
            latest_version = tag_ver

    return str(latest_version)