String C# Tutorial

using System;
class MainClass
{
    public static void Main()
    {
        string test1 = "This is a test string";
        string test2, test3;
        test2 = test1.Insert(15, "AAA ");
        test3 = test1.ToUpper();
       Console.WriteLine("test1: '{0}'", test1);
        Console.WriteLine("test2: '{0}'", test2);
        Console.WriteLine("test3: '{0}'", test3);
        if (test1 == test3)
            Console.WriteLine("test1 is equal to test3");
        else
            Console.WriteLine("test1 is not equal to test3");
       
    }
}
test1: 'This is a test string'
test2: 'This is a test AAA string'
test3: 'THIS IS A TEST STRING'
test1 is not equal to test3