Question

I’ve isolated the behaviour into the following test case. I’d be grateful to anyone who can tell me how to expect/verify a property set for a List<T> property – it appears there’s something going on inside It.Is<T>(predicate) that isn’t making a whole lot of sense to me right now. Sample code will run as a console app from VS2008 – you’ll need to add a reference to Moq 2.6 (I’m on 2.6.1014.1) – please try uncommenting the different ExpectSet statements to see what’s happening…

using System; using Moq; using System.Collections.Generic;  namespace MoqDemo {      public interface IView {         List<string> Names { get; set; }     }      public class Controller {         private IView view;          public Controller(IView view) {             this.view = view;         }          public void PopulateView() {             List<string> names = new List<string>() { 'Hugh', 'Pugh', 'Barney McGrew' };             view.Names = names;         }          public class MyApp {             public static void Main() {                 Mock<IView> mockView = new Mock<IView>();                  // This works - and the expectation is verifiable.                 mockView.ExpectSet(mv => mv.Names);                  // None of the following can be verified.                 // mockView.ExpectSet(mv => mv.Names, It.Is<Object>(o => o != null));                 // mockView.ExpectSet(mv => mv.Names, It.Is<List<string>>(names => names.Count == 3));                 // mockView.ExpectSet(mv => mv.Names, It.IsAny<IList<String>>());                  Controller controller = new Controller(mockView.Object);                 controller.PopulateView();                 try {                     mockView.VerifyAll();                     Console.WriteLine('Verified OK!');                 } catch (MockException ex) {                     Console.WriteLine('Verification failed!');                     Console.WriteLine(ex.Message);                 }                 Console.ReadKey(false);             }         }     } } 

Answer 1

I’m not using the very latest version of Moq, so I don’t have an overload of ExpectSet that takes two parameters, but I’ve had some success with this pattern:

mockView.ExpectSet(mv => mv.Names).Callback(n => Assert.That(n != null)); 

The Assert (from NUnit) call in the callback will throw an exception if the value assigned to .Names doesn’t match the predicate. It does make it hard to trace when a test fails, though. I agree that the ability to pass an It.Is or It.IsAny as the second parameter would be handy.