code: public static void assertXMLIdentical(String msg, Diff diff, boolean assertion) {
          if (assertion != diff.identical()) {
              fail(getFailMessage(msg, diff));
          }
      }
docs: Assert that the result of an XML comparison is or is not identical
  @param msg Message to display if assertion fails
  @param diff the result of an XML comparison
  @param assertion true if asserting that result is identical