public void WhenExecutingEmptyEquation_ThenResultShouldSayNothing()
        {
            // Arrange
            var vm = new CalculatorViewModel(new EquationParser(), new Calculator());
            vm.Equation = "";

            // Act
            vm.Execute();

            // Assert
            Assert.AreEqual("Nothing", vm.Result);
        }
        public void WhenExecutingAnAddEquation_ThenResultShouldAddTheTwoNumbers()
        {
            // Arrange
            var vm = new CalculatorViewModel(new EquationParser(), new Calculator());
            vm.Equation = "1+2";

            // Act
            vm.Execute();

            // Assert
            Assert.AreEqual("3", vm.Result);
        }