How to read two XML files using XMLUnit

Question

I am new to XML.After a lot of search i found XMLUnit to do that but the problem am getting is : whenever i change the contents of xml file to simple string text and try to execute the code ,it still shows green in junit test which it should not do although it is throwing an exception but my requirement is the signal should be red even the files are not in proper xml format.Enclosing my work for so far.

package mypack;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.List;

import org.custommonkey.xmlunit.DetailedDiff;
import org.custommonkey.xmlunit.Diff;
import org.custommonkey.xmlunit.XMLTestCase;
import org.custommonkey.xmlunit.XMLUnit;
import org.junit.Test;
import org.xml.sax.SAXException;

public class MyXMLTestCase extends XMLTestCase {


    enter code here
    @Test
    public void testMyXmlTestCase() {
        FileReader expected = null;
        FileReader output = null;
        try {
            expected = new FileReader("D:/vivek.xml");
            output = new FileReader("D:/rahul.xml");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

        XMLUnit.setNormalizeWhitespace(Boolean.TRUE);
        try {
            Diff diff = new Diff(expected,output);
            // assertTrue("XMLSimilar"+diff.toString(),diff.similar());
            //assertTrue("XMLIdentical"+diff.toString(),diff.identical());
            DetailedDiff mydiff = new DetailedDiff(diff);
            List allDifferences = mydiff.getAllDifferences();
            assertEquals(mydiff.toString(), 0, allDifferences.size());

        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}