protected void checkInvalidString(String str) {
    if (ERRONEOUS_STRING_FOR_FROM_DELTA.equals(str)) {
      fromDeltaFailure++;
      throw new InvalidDeltaException("Delta could not be applied. " + this);
    }
  }
**************************************************************************
Below methods are not part of standard Delta implementation but are used for testing purpose.
geode-junit/src/main/java/org/apache/geode/DeltaTestImpl.java