Test callback delegate with Rhino.Mocks

Here is the case to test callback delegate by using Rhino.Mocks.

The following service class has a method with a delegate callback as parameter to get a list of products:

// somethere delegate is defined, Product is an another class
public delegate void RetrieveProductListCallback(
 bool success, List<product> products);

// service class
public class ProductService
{
  // ...
  List<product> RetrieveProducts(
   RetrieveProductCallbackHander callback)
  { //...
  }
}

// Define a method which is used as delegate handler
private void ProductListHandler(bool success,
  List<Product> products)
{   // ...
}

RetrieveProductListCallback callback = ProductListHandler;

_productService.RetrieveProducts(callback);

What I want to test this service's callback event. There were no direct information about this issue. I spent several hours googling information on web and tested many different ways. Finally I found a way to test the callback. Here is the summary of the tricks: using Last.Callback and Predicate to do the test. Here are some codes for the test:

[test]
public void ShouldGetAllProudctsFromService()
{
  List<Product> products = new List<Product>();
  // add some products to the list
  bool success = true;
  // define a none-null callback
  RetrieveProductListCallback callback = delegate {};

  using (Mocks.Record())
  {
    // expect to call method with callback
    _productService.
      RetrieveProudcts(callback);
    // Here is the trick to set up callback
    // to be called
    LastCall.Callback(
      (Predicate<RetrieveProjectListCallback>)
      delegate(
      RetrieveProductListCallback callbackhander)
      {
        if (callbackhander != null)
        {
           callbackhander(success, products);
        }
        return true;
      });

      // ...
   }

   using (Mocks.Playback())
   {
     // ... assert
   }
 }
}