void subject_non_null() {
            Subject s = new Subject();
            TestCredentials creds = new TestCredentials("X", false, false, s, false);
            assertSame(s, creds.getSubject());
        }

        @Test
        @DisplayName("allows null subject")
        void subject_null() {
            TestCredentials creds = new TestCredentials("X", false, false, null, false);
            assertNull(creds.getSubject());