code: public static void assertXpathExists(String xPathExpression, 
                                           String inXMLString)
          throws IOException, SAXException, XpathException {
          Document inDocument = XMLUnit.buildControlDocument(inXMLString);
          assertXpathExists(xPathExpression, inDocument);
      }
docs: Assert that a specific XPath exists in some given XML
  @param xPathExpression
  @param inXMLString
  @see XpathEngine which provides the underlying evaluation mechanism