Fakes Framework Replace Function Implementation

Visual Studio 2012 introduces Fakes Framework. Currently I need to find a testing framework and Fakes is one of my choice. I cannot find any good tutorial, hopefully this one can give a quick start.

First the C# code for testing is:

 public interface IStock  
   {  
     int F();  
     int F1(int i);  
   }  
   public class Stock : IStock  
   {  
     public int F()  
     {  
       return 1;  
     }  
     public int F1(int i)  
     {  
       return i + 1;  
     }  
   }  

After creating the Test Project from Visual Studio, you can replace the F1 implementation with a new function.

 using (var context = ShimsContext.Create())  
       {  
         System.Fakes.ShimDateTime.NowGet = () => new DateTime();  
         var dt = DateTime.Now;  
         var shim = new ClassLibrary1.Fakes.ShimStock();  
         shim.F = () => 7;  
         var x = shim.Instance.F(); //x is 7 instead of 1  
       }