Question

I am currently trying to learn DI & Mocking, with Unity and NSubstitute. I am also using an automocking extension taken from this question: Is this possible with Unity (Instead of Castle Windsor)?

In my unit test below I am trying to set an NSubstitute return value of 10 from my method Add(). However when debugging through the controller call the assigned value is the default 0 rather than the expected 10. The proxy does not seem to be intercepting the method call.

I suspect this is caused by not registering my Types/container correctly, anybody able to point me in the right direction?

[TestFixture]
public class ApplicationControllerTests
{
    private IUnityContainer _container;
    private ApplicationController _controller;
    private ISampleService _sampleService;

    [SetUp]
    public void SetUp()
    {
        _container = new UnityContainer().AddExtension(new AutoMockingContainerExtension());
        _controller = _container.Resolve<ApplicationController>();
        _sampleService = _container.Resolve<ISampleService>();
    }

    [Test]
    public void TestSampleService()
    {
        // This line is not working
        _sampleService.Add(Arg.Any<int>(), Arg.Any<int>()).Returns(10);

        var result = _controller.Index();

        _sampleService.Received().Add(Arg.Any<int>(), Arg.Any<int>());
    }
}

public class AutoMockingContainerExtension : UnityContainerExtension
{
    protected override void Initialize()
    {
        var strategy = new AutoMockingBuilderStrategy(Container);

        Context.Strategies.Add(strategy, UnityBuildStage.PreCreation);
    }

    class AutoMockingBuilderStrategy : BuilderStrategy
    {
        private readonly IUnityContainer _container;

        public AutoMockingBuilderStrategy(IUnityContainer container)
        {
            _container = container;
        }

        public override void PreBuildUp(IBuilderContext context)
        {
            var key = context.OriginalBuildKey;

            if (key.Type.IsInterface && !_container.IsRegistered(key.Type))
                context.Existing = CreateSubstitute(key.Type);
        }

        private static object CreateSubstitute(Type type)
        {
            return Substitute.For(new[] { type }, null);
        }
    }
}

And my controller code

public class ApplicationController : BaseController
{
    private readonly ISampleService _sampleService;

    public ApplicationController(ISampleService sampleService)
    {
        _sampleService = sampleService;
    }

    public ActionResult Index()
    {
        var result = _sampleService.Add(2, 3);

        // result is 0, expected 10 ??

        return View();
    }
}

public interface ISampleService
{
    int Add(int first, int second);
}

public class SampleService : ISampleService
{
    public int Add(int first, int second)
    {
        return first + second;
    }
}

Answer 1

Actually Tormod is right the problem is that the AutoMockingBuilderStrategy returns a different mock instance every time when somebody requests an ISampleService form the container.

So there is a bug in my original implementation namely the AutoMockingBuilderStrategy doesn’t store the created mocks:

Here is a fixed version:

public class AutoMockingContainerExtension : UnityContainerExtension
{
    protected override void Initialize()
    {
        var strategy = new AutoMockingBuilderStrategy(Container);

        Context.Strategies.Add(strategy, UnityBuildStage.PreCreation);
    }

    class AutoMockingBuilderStrategy : BuilderStrategy
    {
        private readonly IUnityContainer container;
        private readonly Dictionary<Type, object> substitutes 
           = new Dictionary<Type, object>();

        public AutoMockingBuilderStrategy(IUnityContainer container)
        {
            this.container = container;
        }

        public override void PreBuildUp(IBuilderContext context)
        {
            var key = context.OriginalBuildKey;

            if (key.Type.IsInterface && !container.IsRegistered(key.Type))
            {
                context.Existing = GetOrCreateSubstitute(key.Type);
                context.BuildComplete = true;
            }
        }

        private object GetOrCreateSubstitute(Type type)
        {
            if (substitutes.ContainsKey(type))
                return substitutes[type];

            var substitute = Substitute.For(new[] {type}, null);

            substitutes.Add(type, substitute);

            return substitute;
        }
    }
}