code: private static void assertXpathEquality(String controlXpath,
                                              Document controlDocument,
                                              String testXpath,
                                              Document testDocument,
                                              boolean equal)
          throws XpathException {
          XpathEngine xpath = XMLUnit.newXpathEngine();
          Diff diff = new Diff(asXpathResultDocument(XMLUnit.newControlParser(),
                                                     xpath.getMatchingNodes(controlXpath,
                                                                            controlDocument)),
                               asXpathResultDocument(XMLUnit.newTestParser(),
                                                     xpath.getMatchingNodes(testXpath,
                                                                            testDocument)));
          assertXMLEqual(diff, equal);
      }
docs: Assert that the node lists of two Xpaths in two documents are
  equal or not.
  @param controlXpath
  @param testXpath
  @param controlDocument
  @param testDocument
  @param equal whether the values should be equal.
  @see XpathEngine