In my unit test how can I verify that an event is raised by the mocked object.

I have a View(UI) --> ViewModel --> DataProvider --> ServiceProxy. ServiceProxy makes async call to serivce operation. When async operation is complete a method on DataProvider is called (callback method is passed as a method parameter). The callback method then raise and event which ViewModel is listening to.

For ViewModel test I mock DataProvider and verify that handler exists for event raised by DataProvider. When testing DataProvider I mock ServiceProxy, but how can I test that callback method is called and event is raised.

I am using RhinoMock 3.5 and AAA syntax

Thanks

-- DataProvider --

public partial class DataProvider
{
    public event EventHandler<EntityEventArgs<ProductDefinition>> GetProductDefinitionCompleted;

    public void GetProductDefinition()
    {
        var service = IoC.Resolve<IServiceProxy>();
        service.GetProductDefinitionAsync(GetProductDefinitionAsyncCallback);
    }

    private void GetProductDefinitionAsyncCallback(ProductDefinition productDefinition, ServiceError error)
    {
        OnGetProductDefinitionCompleted(this, new EntityEventArgs<ProductDefinition>(productDefinition, error));
    }

    protected void OnGetProductDefinitionCompleted(object sender, EntityEventArgs<ProductDefinition> e)
    {
        if (GetProductDefinitionCompleted != null)
            GetProductDefinitionCompleted(sender, e);
    }
}

-- ServiceProxy --

public class ServiceProxy : ClientBase<IService>, IServiceProxy
{
    public void GetProductDefinitionAsync(Action<ProductDefinition, ServiceError> callback)
    {
        Channel.BeginGetProductDefinition(EndGetProductDefinition, callback);
    }

    private void EndGetProductDefinition(IAsyncResult result)
    {
        Action<ProductDefinition, ServiceError> callback =
            result.AsyncState as Action<ProductDefinition, ServiceError>;

        ServiceError error;
        ProductDefinition results = Channel.EndGetProductDefinition(out error, result);

        if (callback != null)
            callback(results, error);
    }
}