How to use the hacking.checks.git.GitCheck function in hacking

'([Bb]ug|[Ll][Pp])[\s\#:]*(\d+)|'
        '([Bb]lue[Pp]rint|[Bb][Pp])[\s\#:]*([A-Za-z0-9\\-]+)')

    def run_once(self):
        title = self._get_commit_title()

        # NOTE(jogo) if match regex but over 3 words, acceptable title
        if (title and self.GIT_REGEX.search(title) is not None
                and len(title.split()) <= 3):
            return (1, 0,
                    "H801: git commit title ('%s') should provide an accurate "
                    "description of the change, not just a reference to a bug "
                    "or blueprint" % title.strip(), self.name)


class OnceGitCheckCommitTitleLength(GitCheck):
    """Check git commit message length.

    HACKING recommends commit titles 50 chars or less, but enforces
    a 72 character limit

    H802 Title limited to 72 chars
    """
    name = "GitCheckCommitTitleLength"

    def run_once(self):
        title = self._get_commit_title()

        if title and len(title) > 72:
            return (
                1, 0,
                "H802: git commit title ('%s') should be under 50 chars"

if not os.path.exists(gitdir):
            return None

        # Get title of most recent commit
        subp = subprocess.Popen(
            ['git', 'log', '--no-merges', '--pretty=%s', '-1'],
            stdout=subprocess.PIPE)
        title = subp.communicate()[0]

        if subp.returncode:
            raise Exception("git log failed with code %s" % subp.returncode)
        return title.decode('utf-8')


class OnceGitCheckCommitTitleBug(GitCheck):
    """Check git commit messages for bugs.

    OpenStack HACKING recommends not referencing a bug or blueprint in first
    line. It should provide an accurate description of the change
    H801
    """
    name = "GitCheckCommitTitleBug"

    # From https://github.com/openstack/openstack-ci-puppet
    #       /blob/master/modules/gerrit/manifests/init.pp#L74
    # Changeid|bug|blueprint
    GIT_REGEX = re.compile(
        r'(I[0-9a-f]{8,40})|'
        '([Bb]ug|[Ll][Pp])[\s\#:]*(\d+)|'
        '([Bb]lue[Pp]rint|[Bb][Pp])[\s\#:]*([A-Za-z0-9\\-]+)')