How to use the buku.ExtendedArgumentParser.prompt_help function in buku

def test_prompt_help():
    """test method."""
    file = mock.Mock()
    import buku
    buku.ExtendedArgumentParser.prompt_help(file)
    assert len(file.write.mock_calls) == 1

# No new results fetched beyond this point
        new_results = False

        # toggle deep search with 'd'
        if nav == 'd':
            deep = not deep
            if deep:
                print('deep search on')
            else:
                print('deep search off')

            continue

        # Show help with '?'
        if nav == '?':
            ExtendedArgumentParser.prompt_help(sys.stdout)
            continue

        # Edit and add or update
        if nav == 'w' or nav.startswith('w '):
            edit_at_prompt(obj, nav)
            continue

        # Append or overwrite tags
        if nav.startswith('g '):
            unique_tags, dic = obj.get_tag_all()
            _count = obj.set_tag(nav[2:], unique_tags)
            if _count == -1:
                print('Invalid input')
            else:
                print('%d updated' % _count)
            continue