Tukukkk

How can I mock a Managed Extensibility Framework (MEF) import into an ExportFactory[IMyType[T]], using mocks of IMyType[T] (being itself a generic interface)? Or, in general, specify instances to be returned by the ExportFactory, which can't be created with a constructor alone?

Moq can't create a mock instance directly, as far as I know. I want an alternative to implementing the whole interface, which may be much larger and change, while I don't want to change the test.

I once found a very complex ExportProvider code, with key-value strings, which didn't work if the generic type of the ExportFactory[T] was itself generic.

// actual generic type is meaningless here, but it is a generic interface

public interface IMyType<T>

{

    string GetMessage();

}



public class FactoryImporter<T>

{

    [Import]

    ExportFactory<IMyType<T>> MyTypeFactory {get;set;}

} 



public class Tester

{

    public void TestFactoryImporter()

    {

        Func<IMyType<string>> createMockFunc = () =>

        {

            var mock = new Mock<IMyType<string>>();

            mock.Setup(m => m.GetMessage()).Returns("I'm a mocked IMyType<string>");

            return mock.Object;

        }



        var regBuilder = new RegistrationBuilder();



        // pseudo-code, how to do this in reality?

        regBuilder.ForType<IMyType<string>>().CreateInstance(createMockFunc);



        var catalog = new AggregateCatalog();

        var appCatalog = new ApplicationCatalog(regBuilder);

        catalog.Catalogs.Add(appCatalog);

        var container = new CompositionContainer(catalog);



        var factoryImporter = new FactoryImporter<string>();

        container.ComposeParts(factoryImporter);



        Assert.AreEqual(

            "I'm a mocked IMyType<string>",

            factoryImporter.MyTypeFactory.GetExport().Value.GetMessage());

    }

}