def METHOD_NAME(dataset_dir: str):
    """Create mocked dataset for a sub directory.
    Args:
        dataset_dir (str): the path of the sub directory.
        The structure is: audio_type/speaker_id/chapter_id/filename.flac
    """
    mocked_data = []
    sample_rate = 16000  # 16kHz
    seed = 0
    for audio_type in ["clean", "other"]:
        for speaker_id in range(5):
            for chapter_id in range(3):
                file_path = os.path.join(dataset_dir, audio_type, str(speaker_id), str(chapter_id))
                os.makedirs(file_path, exist_ok=True)
                trans_content = []
                for utterance_id in range(3):
                    sample = _save_sample(file_path, speaker_id, chapter_id, utterance_id, sample_rate, seed)
                    trans_content.append(f"{sample[3]}-{sample[4]}-{sample[5]:04d} {sample[2]}")
                    mocked_data.append(sample)
                    seed += 1
                trans_filename = f"{speaker_id}-{chapter_id}.trans.txt"
                trans_path = os.path.join(file_path, trans_filename)
                with open(trans_path, "w") as f:
                    f.write("\n".join(trans_content))
    return mocked_data