}

    @Test
    @DisplayName("isAnonymous: depends on subject presence and super")
    void isAnonymous_behaviour() {
        Kerb5Authenticator anon = new Kerb5Authenticator((Subject) null);
        assertTrue(anon.isAnonymous(), "Null subject with default super should be anonymous");

        Kerb5Authenticator nonAnon = new Kerb5Authenticator(new Subject());
        assertFalse(nonAnon.isAnonymous());

    static Stream<Arguments> implementations() {
        SessionSetupHandler anon = new SessionSetupHandler() {
            // no methods to implement (marker interface)
        };
        SessionSetupHandler mock = mock(SessionSetupHandler.class);
        return Stream.of(Arguments.of(anon), Arguments.of(mock));
    }

    @Test
    @DisplayName("Class is a public interface in expected package")