How to mock Autofaq interface with Moq, when an extension method is called

Question

Using C#/Autofac/Moq: I have this class:

public class MyService
{
    private readonly IlifetimeScope _scope;

    public MyService(ILifetimeScope scope)
    {
        _scope = scope;
    }

    public void DoWork()
    {
         var dbContext = _scope.Resolve<IDataContext>();
    }
}

This works at runtime. However, I can't unit test it, since I cannot mock the Resolve() method. It is an extension method.

What's the best way to be able to mock it? The obvious thing would be to inject the IDataContext in the constructor instead of the ILifetimeScope, but for various reasons I cannot.

So, would it work to inject a Func instead?

public class MyService
{
    private readonly Func<IDataContext> _dbContext;

    public MyService(Func<IDataContext> dbContext)
    {
        _dbContext = dbContext;
    }

    public void DoWork()
    {
         var ctxt = _dbContext();
         // do stuff
    }
}

As in: I can mock it, but will Autofac figure out how to inject the correct parameter to the ctor? Or is there a better/simpler way to do this?

I am curious what the "various reasons you cannot" use constructor injection are, which have led you to use the service locator anti-pattern. You have acknowledged that it is a possibility, but why not work through the issues to do it right instead of trying to find a workaround for tests (that probably shouldn't even need to reference Autofac)? I find it useful to consider what would happen if you remove the reference to the DI container - if anything outside of the composition root would break if you did, you are probably tightly coupled to the container. — NightOwl888, May 23 '17 at 20:30
Use the [Autofac.Extras.Moq](https://autofaccn.readthedocs.io/en/latest/integration/moq.html) nuget package. — Shahin Dohan, May 06 '19 at 14:41

score 1 · Answer 1 · answered Mar 27 '18 at 23:22

I know doing this is not ideal, but in some more uncommon scenarios it may be necessary.

I had a situation that was a bit different. I have a method that needs to create a new context on demand, it is a console app so it's not like core's MVC that would begin a new lifetimescope per request. So I got the Autofac/Moq extension: http://autofac.readthedocs.io/en/latest/integration/moq.html

This will allow you to tell the container what instance to return for a particular interface.

Then you can pretty much do it like this:

[Fact]
public void Test()
{
    using (var mock = AutoMock.GetLoose())
    {
        var moqMockMe = new Mock<MockMe>();
        moqMockMe.Setup(s => s.AmIMocked()).Returns("Yes");
        mock.Provide(moqMockMe.Object);

        var lifeTimeScope = mock.Create<ILifetimeScope>();
        using (var scope = lifeTimeScope.BeginLifetimeScope())
        {
            var mockMeInsideScope = scope.Resolve<MockMe>();
            var actual = mockMeInsideScope.AmIMocked();
            Assert.Equal("Yes", actual);
        }
    }
}

public interface MockMe
{
    string AmIMocked();
}

public class MockMeImpl : MockMe
{
    public string AmIMocked()
    {
        return "No";
    }
}

So in case the service you're calling has a method that begins a new lifetimescope, you can mock the result and test it by using this fake ILifeTimeScope created in the example above.

This particular example does not demonstrate resolving a dependency from a child lifetime scope, which appears to be an open issue: https://github.com/autofac/Autofac.Extras.Moq/issues/43 — John Zabroski, Oct 28 '22 at 21:09

score 1 · Answer 2 · edited Dec 29 '21 at 04:02

This is far from ideal but it's possible to examine the internals of the extension method and mock the actual non-extension calls it makes. Obviously this is fragile in the sense that a new version of autofac might break your tests.

For me, the following was successful (autofac v4.X):

Mock<IComponentRegistry> componentRegistryMock = new Mock<IComponentRegistry>();
IComponentRegistry componentRegistry = componentRegistryMock.Object;
IComponentRegistration componentRegistration = new Mock<IComponentRegistration>().Object;

componentRegistryMock
    .Setup(x => x.TryGetRegistration(It.IsAny<Service>(), out componentRegistration))
    .Returns(true);

lifetimeScopeMock
    .Setup(x => x.ComponentRegistry)
    .Returns(componentRegistry);

lifetimeScopeMock
    .Setup(x => x.ResolveComponent(componentRegistration, It.IsAny<IEnumerable<Parameter>>()))
    .Returns(dataService);

score 1 · Answer 3 · answered Oct 15 '20 at 11:19

This worked for me:

var mock = AutoMock.GetLoose(builder => {
    var dbContext = new Mock<IDataContext>();
    dbContext.Setup(d => d.Something())
        .Returns(whatever...);

    builder.RegisterInstance(dbContext.Object).As<IDataContext>();
});

var myService = mock.Container.Resolve<MyService>();

score 1 · Answer 4 · answered Oct 28 '22 at 23:36

The secret sauce is to use Autofac.Extras.Moq nuget package.

Pre v5.0.0:

AutoMock.Provide(new Mock<IService>().Object);

Provide was removed in v5.0.0

v5.0.0 and later:

var mock = AutoMock.GetLoose(cb =>
                             cb.RegisterInstance(new Mock<IService>().Object));

v5.0.0 and later, using AutoFixture.AutoMoq:

If you are using AutoFixture.AutoMoq, then the following will work as an extension of the above approach:

var mock = AutoMock.GetLoose(cb =>
                             cb.RegisterInstance(new Mock<IService>().Object));

var lifetimeScope = mock.Create<ILifetimeScope>();
Fixture.Inject(lifetimeScope);

score -1 · Answer 5 · answered May 26 '17 at 11:35

-1

For anyone else looking at this; the Func<T> trick worked for me.

answered May 26 '17 at 11:35

Henrik Oscarsson

147
1
11

score -3 · Answer 6 · answered May 23 '17 at 19:59

-3

Have you considered simply mocking the scope?

public class Test
{
    private readonly Mock<ILifetimeScope> _scopeMock;
    private readonly Mock<IDataContext> _contextMock;

    public Test()
    {
        _contextMock = new Mock<IDataContext>();
        _scopeMock = new Mock<ILifetimeScope>();
        _scopeMock.Setup( s => s.Resolve<IDataContext>() ).Returns( _contextMock.Object );
    }
}

answered May 23 '17 at 19:59

yoger

282
3
15

8

As I stated in my question, the Resolve() method cannot be mocked, as it is an extension method. – Henrik Oscarsson May 24 '17 at 04:56

How to mock Autofaq interface with Moq, when an extension method is called

6 Answers6

Pre v5.0.0:

v5.0.0 and later:

v5.0.0 and later, using AutoFixture.AutoMoq:

Linked