public ActionResult Index(AdditionViewModel model)
        {
            if (ModelState.IsValid)
            {
                ModelState.Clear();
                model.Result = model.First + model.Second;
            }

            return View(model);
        }
        public void TestPostIndex()
        {
            int? expected = TestContext.DataRow["Expected"] as int?;
            AdditionViewModel model = new AdditionViewModel()
            {
                First = TestContext.DataRow["First"] as int?,
                Second = TestContext.DataRow["Second"] as int?
            };
            AdditionController testSubject = new AdditionController();

            ViewResult result = testSubject.Index(model) as ViewResult;

            Assert.IsNotNull(result.Model);
            Assert.IsInstanceOfType(result.Model, typeof(AdditionViewModel));
            Assert.AreEqual(expected, ((AdditionViewModel)result.Model).Result);
        }