def METHOD_NAME():
    word_str_ser_ls = ["probate", "rate", "cease", "ones"]
    word_str_ser = cudf.Series(word_str_ser_ls)
    expect = ["probat", "rate", "ceas", "ones"]
    st = PorterStemmer()
    got = st._step5a(word_str_ser)
    assert list(got.to_pandas().values) == expect
    # mask test
    expect = expect[:-2] + ["cease", "ones"]
    mask = cudf.Series([True] * (len(expect) - 2) + [False] * 2)
    got = st._step5a(word_str_ser, mask)
    assert list(got.to_pandas().values) == expect