using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var tests = new List<Test>

        {

            new Test {Name = "Bob"},

            new Test {Name = "George"},

            new Test {Name = "Harry"}

        };

        var result = tests.Select((x, index) => {x.Id = index; return x;});

        foreach (var test in result)

        {

            Console.WriteLine(test.Id + ": " + test.Name);

        }

    }

    public class Test

    {

        public int Id {get;set;}

        public string Name {get;set;}

    }

}