code: public void addGenerator( String functionName, ITestCaseGenerator generator)
      {
      String functionKey = getFunctionKey( functionName);
      if( generators_.containsKey( functionKey))
        {
        throw new IllegalArgumentException( "Generator already defined for function=" + functionName);
        }
  
      if( generator != null)
        {
        generators_.put( functionKey, generator);
        }
      }
docs: Adds a new test case generator for the given system function.