Moq, ref, setup and queue

Question

I have a method I am testing which requires a 'ref' parameter. I would like this parameter to return a different value each time the method is called (I expect to be 10 times in this test). I cannot think about how to mock this. Here is what I have so far - which doesn't compile:

var refParentMenuId = It.Is<int>(i => new Queue<int>( new int [] { 1,2,3,4,5,6,7,8,9,10 }).Dequeue);

this.MockMenuRepository.Setup(m => m.Create(It.IsAny<string>, It.IsAny<int>(), It.IsAny<int>(), It.IsAny<int>(), ref refParentMenuId));

I would like to stick using a ref rather than returning a struct as I think this way is more intuitive.

score 3 · Accepted Answer · edited May 23 '17 at 11:53

Specifying behaviour for ref arguments is not supported out of the box, however it is possible to add your own extension methods to support this behaviour. There is a solution posted here.

For your example, the test looks a little like this:

[TestClass]
public class RefUnitTests
{
    private Queue<int> queue = new Queue<int>(new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });

    [TestMethod]
    public void TestRefArgs()
    {
        int inputInt = 0;

        var repository = new Mock<IRepository>();

        repository
            .Setup(r => r.Create(It.IsAny<string>(), It.IsAny<int>(), It.IsAny<int>(), It.IsAny<int>(), ref inputInt))
            .Returns(0)
            .IgnoreRefMatching()
            .RefCallback<string, int, int, int, int, IRepository>(new MoqExtension.RefAction<string, int, int, int, int>(ReportInfoRefCallBackAction));

        int actualInt = -1;

        for (int i = 1; i <= 10; i++)
        {
            repository.Object.Create(string.Empty, 1, 2, 3, ref actualInt);

            // Assert that we are really dequeuing items
            Assert.AreEqual(i, actualInt);
        }
    }

    public void ReportInfoRefCallBackAction(string a, int b, int c, int d, ref int refInt)
    {
        // You can also assert on the incoming ref value here if you wish, I wrote
        // it to the console so that you can see it is changing.
        Console.WriteLine(refInt);
        refInt = queue.Dequeue();
    }
}

You didn't define the repository you are testing, so I used an interface which looks similar:

public interface IRepository
{
    int Create(string arg1, int arg2, int arg3, int arg4, ref int arg);
}

Here is the code required to extend Moq, adapted from the link above:

public static class MoqExtension
{
    public delegate void RefAction<TParam1, TParam2, TParam3, TParam4, TRef>(TParam1 param1, TParam2 param2, TParam3 param3, TParam4 param4, ref TRef refVal1);

    public static IReturnsResult<TMock> RefCallback<TParam1, TParam2, TParam3, TParam4, TRef, TMock>(
       this ICallback mock,
       RefAction<TParam1, TParam2, TParam3, TParam4, TRef> action) where TMock : class
    {
        mock.GetType().Assembly
               .GetType("Moq.MethodCall")
               .InvokeMember("SetCallbackWithArguments",
               BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Instance,
               null,
               mock,
               new object[] { action });

        return mock as IReturnsResult<TMock>;
    }

    public static ICallback IgnoreRefMatching(this ICallback mock)
    {
        try
        {
            FieldInfo matcherField = typeof(Mock).Assembly.GetType("Moq.MethodCall").GetField("argumentMatchers", BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.SetField | BindingFlags.Instance);

            IList argumentMatchers = (IList)matcherField.GetValue(mock);
            Type refMatcherType = typeof(Mock).Assembly.GetType("Moq.Matchers.RefMatcher");
            FieldInfo equalField = refMatcherType.GetField("equals", BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.SetField | BindingFlags.Instance);

            foreach (object matcher in argumentMatchers)
            {
                if (matcher.GetType() == refMatcherType)
                    equalField.SetValue(matcher, new Func<object, bool>(delegate(object o) { return true; }));
            }

            return mock;
        }
        catch (NullReferenceException)
        {
            return mock;
        }
    }
}

Moq, ref, setup and queue

1 Answers1