Question

I’m trying to mock an method to a third-party library using moq.
The problem is that the method I’m mocking returns an object that is internal inside this framework, and thus I cannot instanciate this.

In the example below both the ChangeCollection and the ItemChange is internal, and I get the error: ‘Cannot access internal constructor ‘ChangeCollection’ here’

I’m having problems figuring out a good solution for this, does someone have any ideas?

[TestMethod]
public void GetItemsForExistingEMails_should_call_GetItems_atleast_once()
{
    ewsMock = new Mock<IEwsIntegration>();
    ewsMock.Setup(e => e.GetItems()).Returns(new ChangeCollection<ItemChange>);
    var emailService = new EmailService(ewsMock.Object);

    var items = emailService.GetItemsForExistingEMails();

    ewsMock.Verify(e => e.GetItems(), Times.AtLeast(1));
    Assert.AreEqual(0, items.Count());
}

public interface IEwsIntegration
{
    ChangeCollection<ItemChange> GetItems();
}

Answer 1

I think you can get away with returning IEnumerable<ChangeItem> in your interface. It seems like ChangeCollection is just an implementation of IEnumerable<T>.

public interface IEwsIntegration
{
    IEnumerable<ItemChange> GetItems();
}

Then you can simply return a list in your setup

ewsMock.Setup(e => e.GetItems()).Returns(new List<ItemChange>());

Update:

Since you have to use properties defined only on the concrete class, you have to create an adapter.

First create an interface with the members from the concrete class.

public interface IChangeCollection<T> : IEnumerable<T>
{
    bool MoreChangesAvailable { get; }
    string SyncState { get; }
}

Make sure you return this type from your interface:

public interface IEwsIntegration
{
    IChangeCollection<ItemChange> GetItems();
}

Then you have to create an implementation of IChangeCollection<T> which will simply direct calls to an instance of ChangeCollection.

public class ChangeCollectionAdapter<T> : IChangeCollection<T>
{
    private readonly ChangeCollection _changeCollection;

    public ChangeCollectionAdapter(ChangeCollection changeCollection)
    {
        _changeCollection = changeCollection;
    }

    public bool MoreChangesAvailable 
    { 
        get { return _changeCollection.MoreChangesAvailable; }
    }

    //other members
}