assertThrows(IOException.class, () -> new NegTokenTarg(bad), "Malformed byte[] should cause IOException");
    }

    @Test
    @DisplayName("mechanism token empty array – preserved after round‑trip")
    void testEmptyMechanismToken() throws IOException {
        NegTokenTarg nt = new NegTokenTarg();
        nt.setResult(NegTokenTarg.REQUEST_MIC);
        nt.setMechanismToken(new byte[0]); // empty but non‑null