String result = XmlUtil.stripInvalidXMLCharacters(input);
        assertNotNull(result);
        assertTrue(result.contains("Valid XML text 123"));
    }

    public void test_stripInvalidXMLCharacters_withInvalidChars() {
        // Test with invalid control characters (0x1-0x8, 0xB, 0xC, 0xE-0x1F)
        String input = "Test\u0001\u0002\u0008Valid\u000B\u000C\u000EText";