}

    public void test_stripInvalidXMLCharacters_empty() {
        // Test empty string
        assertEquals("", XmlUtil.stripInvalidXMLCharacters(""));
    }

    public void test_stripInvalidXMLCharacters_valid() {
        // Test valid XML characters
        String input = "Valid XML text 123\t\n\r";
        String result = XmlUtil.stripInvalidXMLCharacters(input);
        assertNotNull(result);