void getUserDomain_fromSubjectPrincipal() {
            Subject subject = new Subject();
            Principal kp = new KerberosPrincipal("******@****.***");
            subject.getPrincipals().add(kp);

            Kerb5Authenticator auth = new Kerb5Authenticator(subject);
            assertEquals("EXAMPLE.COM", auth.getUserDomain());
        }

        @Test