src/transformers/models/marian/convert_marian_to_pytorch.py/fetch_test_set
def fetch_test_set(test_set_url):
    import wget

    fname = wget.download(test_set_url, "opus_test.txt")
    lns = Path(fname).open().readlines()
    src = lmap(str.strip, lns[::4])
    gold = lmap(str.strip, lns[1::4])
    mar_model = lmap(str.strip, lns[2::4])
    if not (len(gold) == len(mar_model) == len(src)):
        raise ValueError(f"Gold, marian and source lengths {len(gold)}, {len(mar_model)}, {len(src)} mismatched")
    os.remove(fname)
    return src, mar_model, gold