Question

[using Moq]

I am trying to mock a concrete class and mock a virtual method “Get()” of that class. When testing a method “GetItemsNotNull()” I always get returned null, instead of the return of the mocked function.

Here is the code

---

//SomeClasses.cs
namespace MoQExamples
{
    public abstract class Entity
    {

    }

    public class Abc : Entity
    {

    }

    public interface IRepository<T> where T : Entity
    {
        IQueryable<T> Get();
    }

    public class Repository<T> : IRepository<T> where T : Entity
    {
        private readonly ISession _session;

        public Repository()
        {
            _session = null;
        }

        public Repository(ISession session)
        {
            _session = session;
        }

        protected ISession CurrentSession
        {
            get { return _session; }
        }

        public virtual IQueryable<T> Get()
        {
            return CurrentSession.Query<T>();
        }

    }

    public interface IAbcRepository
    {
        Abc GetItemsNotNull();
    }

    public class AbcRepository : Repository<Abc>, IAbcRepository
    {
        public Abc GetItemsNotNull()
        {
            return Get().FirstOrDefault(abc => abc !=null);
        }
    }
}

---

and here are the test class

namespace MoQExamples
{
    [TestFixture]
    public class SomeClassesTest
    {
        private readonly Mock<AbcRepository> _abcRepositoryMock = new Mock<AbcRepository>(MockBehavior.Strict) { CallBase = true };

        [SetUp]
        public void SetupTest()
        {
            _abcRepositoryMock.Setup(x => x.Get()).Returns(Get);
        }

        public IQueryable<Abc> Get()
        {
            return (new List<Abc>() { new Abc() }) as IQueryable<Abc>;
        }

        [Test]
        public void TestGetItemsNotNull()
        {
            Assert.IsNotNull(_abcRepositoryMock.Object.GetItemsNotNull());
        }

    }
}

the assert alays fails..instead of returning the SomeClassesTest.Get()

thanks for advance guys!

Answer 1

I suspect this is the problem:

return (new List<Abc>() { new Abc() }) as IQueryable<Abc>;

List<T> doesn’t implement IQueryable<T>, so this will always return null. Call AsQueryable to convert it instead:

return new List<Abc>().AsQueryable();

As an aside, this is a reason to prefer casts over as in most situations: if you’d just cast to IQueryable<Abc>, you’d have received an exception at the line which was really causing the problem. You should only use as when it’s not a bug for the conversion to “fail”. An as operator should almost always be followed by a nullity test.

(Note that this behaviour in itself has nothing to do with mocking or Moq. It’s just the behaviour of the as operator…)