How to use the stestr.output.output_stream function in stestr

"""
    try:
        repo = util.get_repo_open(repo_type, repo_url)
    except abstract.RepositoryNotFound as e:
        stdout.write(str(e) + '\n')
        return 1

    try:
        latest_run = repo.get_latest_run()
    except KeyError as e:
        stdout.write(str(e) + '\n')
        return 1

    if subunit_out:
        stream = latest_run.get_subunit_stream()
        output.output_stream(stream, output=stdout)
        # Exits 0 if we successfully wrote the stream.
        return 0
    case = latest_run.get_test()
    try:
        if repo_type == 'file':
            previous_run = repo.get_test_run(repo.latest_id() - 1)
        # TODO(mtreinish): add a repository api to get the previous_run to
        # unify this logic
        else:
            previous_run = None
    except KeyError:
        previous_run = None
    failed = False
    if not pretty_out:
        output_result = results.CLITestResult(latest_run.get_id, stdout,
                                              previous_run)

if args[1]:
        filters = args[1]
    conf = config_file.TestrConf(_args.config)
    cmd = conf.get_run_command(_args, ids, filters)
    try:
        cmd.setUp()
        # List tests if the fixture has not already needed to to filter.
        if filters is None:
            ids = cmd.list_tests()
        else:
            ids = cmd.test_ids
        stream = BytesIO()
        for id in ids:
            stream.write(('%s\n' % id).encode('utf8'))
        stream.seek(0)
        output.output_stream(stream)
        return 0
    finally:
        cmd.cleanUp()

blacklist_file=blacklist_file, whitelist_file=whitelist_file,
        black_regex=black_regex, test_path=test_path, top_dir=top_dir)
    not_filtered = filters is None and blacklist_file is None\
        and whitelist_file is None and black_regex is None
    try:
        cmd.setUp()
        # List tests if the fixture has not already needed to to filter.
        if not_filtered:
            ids = cmd.list_tests()
        else:
            ids = cmd.test_ids
        stream = BytesIO()
        for id in ids:
            stream.write(('%s\n' % id).encode('utf8'))
        stream.seek(0)
        output.output_stream(stream, output=stdout)
        return 0
    finally:
        cmd.cleanUp()