@Test
    public void test_maskSensitiveValue_withPrivate() {
        assertEquals("********", SystemUtil.maskSensitiveValue("PRIVATE_DATA", "sensitive"));
        assertEquals("********", SystemUtil.maskSensitiveValue("private_config", "internal"));
    }

    @Test
    public void test_maskSensitiveValue_safeValues() {
        // These should NOT be masked