Calculator.cs (The add() method)
namespace calculator
{
    public class operations 
    {
        public static int Add(int number1, int number2) 
        {
            return number1 + number2;
        }
    }
}


Program.cs (The test program to test if 1+2 = 3 >.< )
namespace TestCalculator
{
    class Program
    {
        public static void TestSimpleAddition() {
            int total = calculator.operations.Add(1, 2);
            if (total != 3){
                Console.WriteLine("Oops, 1 and 2 does not equal 3");
            }
        }
        static void Main(string[] args){
            TestSimpleAddition();
        }
    }
}

Ive refrenced the Calculator project, and already added using Calculator;