How to use the mike.git_utils.GitError function in mike

def read_file(branch, filename, universal_newlines=False):
    cmd = ['git', 'show', '{branch}:{filename}'.format(
        branch=branch, filename=git_path(filename)
    )]
    p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE,
                 universal_newlines=universal_newlines)
    stdout, stderr = p.communicate()
    if p.wait() != 0:
        raise GitError('unable to read file {!r}'.format(filename),
                       str(stderr))
    return stdout

def get_config(key):
    cmd = ['git', 'config', key]
    p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE, universal_newlines=True)
    stdout, stderr = p.communicate()
    if p.wait() != 0:
        raise GitError('error getting config {!r}'.format(key), stderr)
    return stdout.strip()

def push_branch(remote, branch, force=False):
    cmd = (['git', 'push'] + (['--force'] if force else []) +
           ['--', remote, branch])
    p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE, universal_newlines=True)
    stdout, stderr = p.communicate()
    if p.wait() != 0:
        raise GitError('failed to push branch {} to {}'.format(branch, remote),
                       stderr)

def update_ref(branch, new_ref):
    cmd = ['git', 'update-ref', 'refs/heads/{}'.format(branch), new_ref]
    p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE, universal_newlines=True)
    stderr = p.communicate()[1]
    if p.wait() != 0:
        raise GitError('error updating ref for {}'.format(branch), stderr)

dest = urlparse.urlunsplit(
                        url[:2] + (url[2] + '/',) + url[3:]
                    )
                    self.send_header('Location', dest)
                    self.end_headers()
                    return

                path = posixpath.join(path, 'index.html')
                git_utils.file_mode(self.branch, path)

            self.send_response(200)
            self.send_header('Content-Type', self.guess_type(path))
            self.end_headers()

            return path
        except git_utils.GitError:
            self.send_error(404, 'File not found')
        except Exception:  # pragma: no cover
            self.send_error(500, 'Internal server error')

def file_mode(branch, filename):
    filename = filename.rstrip('/')
    # The root directory of the repo is, well... a directory.
    if not filename:
        return 0o040000

    cmd = ['git', 'ls-tree', '--full-tree', '--', branch, git_path(filename)]
    p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE, universal_newlines=True)
    stdout, stderr = p.communicate()
    if p.wait() != 0:
        raise GitError('unable to read file {!r}'.format(filename), stderr)
    if not stdout:
        raise GitError('file not found')

    return int(stdout.split(' ', 1)[0], 8)

def get_latest_commit(rev, short=False):
    cmd = ['git', 'rev-parse'] + (['--short'] if short else []) + [rev]
    p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE, universal_newlines=True)
    stdout, stderr = p.communicate()
    if p.wait() != 0:
        raise GitError('error getting latest commit', stderr)
    return stdout.strip()

def list_versions(branch='gh-pages'):
    try:
        return Versions.loads(git_utils.read_file(
            branch, versions_file, universal_newlines=True
        ))
    except git_utils.GitError:
        return Versions()

import time
import unicodedata

from enum import Enum

BranchStatus = Enum('BranchState', ['even', 'ahead', 'behind', 'diverged'])


class GitError(Exception):
    def __init__(self, message, stderr=None):
        if stderr:
            message += ': "{}"'.format(stderr.strip())
        super().__init__(message)


class GitBranchDiverged(GitError):
    def __init__(self, branch1, branch2):
        super().__init__('{} has diverged from {}'.format(branch1, branch2))


class GitRevUnrelated(GitError):
    def __init__(self, branch1, branch2):
        super().__init__('{} is unrelated to {}'.format(branch1, branch2))


def git_path(path):
    path = os.path.normpath(path)
    # Fix unicode pathnames on macOS; see
    # .
    if sys.platform == 'darwin':  # pragma: no cover
        if isinstance(path, bytes):
            path = path.decode('utf-8')