private static void TestObserver()
        {
            var temp   = new Thermometer();
            var fun    = new Fan(temp);
            var heater = new Heater(temp);

            temp.UpTemp(new Temperature(-3));
            Console.WriteLine("-------------------");

            temp.UpTemp(new Temperature(30));
            Console.WriteLine("-------------------");

            heater.OnCompleted();

            temp.UpTemp(new Temperature(15));
            Console.WriteLine("-------------------");
        }