docs: def fetch_github_pull_request(destination_directory: str,
                                repository: github_repository.GithubRepository,
                                pull_request_number: int,
                                verbose: bool
                                ) -> prepared_env.PreparedEnv:
      """Uses content from github to create a dir for testing and comparisons.
  
      Args:
          destination_directory: The location to fetch the contents into.
          repository: The github repository that the commit lives under.
          pull_request_number: The id of the pull request to clone. If None, then
              the master branch is cloned instead.
          verbose: When set, more progress output is produced.
  
      Returns:
          Commit ids corresponding to content to test/compare.
      """
  
      branch = 'pull/{}/head'.format(pull_request_number)
      os.chdir(destination_directory)
      print('chdir', destination_directory, file=sys.stderr)
  
      shell_tools.run_cmd(
          'git',
          'init',
          None if verbose else '--quiet',
          out=sys.stderr)
      result = _git_fetch_for_comparison(remote=repository.as_remote(),
                                         actual_branch=branch,
                                         compare_branch='master',
                                         verbose=verbose)
      shell_tools.run_cmd(
          'git',
          'branch',
          None if verbose else '--quiet',
          'compare_commit',
          result.compare_commit_id,
          log_run_to_stderr=verbose)
      shell_tools.run_cmd(
          'git',
          'checkout',
          None if verbose else '--quiet',
          '-b',
          'actual_commit',
          result.actual_commit_id,
          log_run_to_stderr=verbose)
      return prepared_env.PreparedEnv(
          github_repo=repository,
          actual_commit_id=result.actual_commit_id,
          compare_commit_id=result.compare_commit_id,
          destination_directory=destination_directory,
          virtual_env_path=None)