What steps will reproduce the problem? The model interface: public interface IModel { List<IOffer> Offers2 { get; } BindingList<IOffer> Offers { get; } void CreateOffer(); }

The model implementation: public class Model : IModel { private readonly BindingList<IOffer> offers; private readonly List<IOffer> offers2;

public Model()
{
    this.offers = new BindingList<IOffer>();
    this.offers2 = new List<IOffer>();
}

public List<IOffer> Offers2
{
    get { return this.offers2; }
}

public BindingList<IOffer> Offers
{
    get { return this.offers; }
}

public void CreateOffer()
{
    this.Offers.Add(new Offer());      
    this.Offers2.Add(new Offer());
}

}

The model manipulator: public sealed class ModelManipulator { public void Manipulate(IModel model) { model.Offers.Clear(); model.Offers2.Clear();

    model.CreateOffer();
    model.CreateOffer();
    model.CreateOffer();
}

}

The test class (MSTest is used): [TestClass] public class ModelManipulatorFixture { private ModelManipulator testee;

private Mock<IModel> mockModel;

private BindingList<IOffer> offers;
private List<IOffer> offers2;

[TestInitialize]
public void TestInitialize()
{
    this.mockModel = new Mock<IModel>(MockBehavior.Strict);

    this.offers = new BindingList<IOffer>();
    this.offers2 = new List<IOffer>();

    this.mockModel.SetupGet(mock => mock.Offers).Returns(this.offers);
    this.mockModel.SetupGet(mock => mock.Offers2).Returns(this.offers2);

    this.mockModel.Setup(mock => mock.CreateOffer());

    this.testee = new ModelManipulator();
}

[TestMethod]
public void ManipulateModel()
{
    // act
    this.testee.Manipulate(this.mockModel.Object);

    // assert
    this.mockModel.Verify(mock => mock.CreateOffer(), Times.Exactly(3));

    Assert.AreEqual(3, this.offers2.Count);
    Assert.AreEqual(3, this.offers.Count);
}

}

What is the expected output? What do you see instead? Expected is that the assertions do not fail.

What version of the product are you using? On what operating system? Moq 4.0.10827.0, Windows 7 64 Enterprise Bit, Visual Studio 2010 Ultimate

Help

Your line:

this.mockModel.Setup(mock => mock.CreateOffer());

Isn't adding anything to the lists, so obviously those will remain empty.

I do not understand what you mean by "isn't adding anything to the list". The mocked method CreateOffer() in the Model does add items to the lists. public void CreateOffer() { this.Offers.Add(new Offer());
this.Offers2.Add(new Offer()); }

I have also tried the following assertion, wich fails also: Assert.AreEqual(3, this.mockModel.Object.Offers.Count);

Nobody is invoking that method, that's the point. You are mocking IModel, not creating an instance of Model. The mock of an interface doesn't have any behavior.

So, this setup does absolutely nothing:

    this.mockModel.Setup(mock => mock.CreateOffer());