} else {
            assertEquals(SMBProtocolDowngradeException.class.getName() + ": " + message, ex.toString());
        }
    }

    @Test
    void causeConstructor_setsCause_andDerivesMessageFromCauseToString() {
        // Arrange - use a real cause so message is derived from cause.toString()
        Throwable cause = new IllegalStateException("proto mismatch");