public void Sum_ByDefault_ReturnsZero()
        {
            MemCalculatorCh2 calc = MackeCalc();
            int lastSum           = calc.Sum();

            Assert.AreEqual(0, lastSum);
        }
        public void Add_WhenCalled_ChangeSum()
        {
            MemCalculatorCh2 calc = MackeCalc();

            calc.Add(1);
            int lastSum = calc.Sum();

            Assert.AreEqual(1, lastSum);
        }