gistfile1.cs

        protected override void ModifyTargetMethod(MethodDefinition targetMethod)
        {
            // In this example, we are going to redirect all Console.WriteLine calls
            // to the FakeConsole.WriteLine() method
            var module = targetMethod.Module;
            var body = targetMethod.Body;

            // In order to use FakeConsole.WriteLine(), we need to use Cecil to "import"
            // the method into the modified assembly's module
            var writeLine = module.Import(typeof (FakeConsole).GetMethod("WriteLine"));

            var callInstructions = (from instruction in body.Instructions
                                   where instruction.OpCode == OpCodes.Call
                                   select instruction).ToArray();

            foreach(var instruction in callInstructions)
            {
                // Notice how replacing the old method with the FakeConsole.WriteLine() method
                // redirects all console calls to the FakeConsole class
                instruction.Operand = writeLine;
            }
        }