public void It_should_add_and_subtract_numbers()
            {
                var calc = new Calculator();

                int sum = calc.Add(1, 1);
                int answer = calc.Subtract(sum, 1);

                answer.Should().Be(1);
            }
            public void It_should_subtract_numbers()
            {
                var calc = new Calculator();

                int answer = calc.Subtract(2, 1);

                answer.Should().Be(1);
            }