Endless loop when using Automapper on faked IQueryable<T>

Unsure, whether this is an issue with FakeItEasy or Automapper (or even Castle Proxy).

Assuming an IQueryable<Entity> that is mapped using Automapper into an IQueryable<EntityDto> by means of their expression mapping extension. When the original queryable is mocked using FakeItEasy, the enumeration of the mapped queryable never returns. It hogs a CPU at 100%, so I am assuming some kind of endless loop.

public class FakeItEasyTest
{
    private readonly Mapper _mapper;
    private readonly IQueryable<Entity> _queryable;

    public FakeItEasyTest()
    {
        _mapper = new Mapper(new MapperConfiguration(cfg => cfg.CreateMap<Entity, EntityDto>()));
        _queryable = A.Fake<IQueryable<Entity>>();
    }

    [Fact]
    public void CanEnumerateQueryable()
    {
        Assert.Empty(_queryable.ToArray());
    }

    [Fact]
    public void CanEnumerateDataSourceQueryable()
    {
        IQueryable<EntityDto> mappedQueryable = _queryable.UseAsDataSource(_mapper.ConfigurationProvider).For<EntityDto>();

        // never returns!
        Assert.Empty(mappedQueryable.ToArray());
    }

    [Fact]
    public void CanEnumerateProjectedQueryable()
    {
        // never returns!
        IQueryable<EntityDto> mappedQueryable = _queryable.ProjectTo<EntityDto>(_mapper.ConfigurationProvider);
        Assert.Empty(mappedQueryable.ToArray());
    }
}

repo: https://github.com/marcwittke/FakeItEasyVsAutoMapper

[marcwittke]

Works like a charm, @blairconrad . Thanks, I updated the repro-repo that passes all tests now, even when there is an arbitrary interface faked that has a method returning IQueryable.

I made an attempt with a dummy factory before, but obviously I was missing something. Well, it got pretty late yesterday…

Thanks!

[blairconrad]

@marcwittke, I’m sure you’ll get your configuration working, but if you’re interested, I stole some minutes to implement a DummyFactory that you might enjoy. It seemed to do the trick for me.

public class DummyQueryableFactory : IDummyFactory
{
    public bool CanCreate(Type type)
    {
        if (type.IsGenericType)
        {
            var queryableContentType = type.GetGenericArguments()[0];
            var queryableTypeDefinition = typeof(IQueryable<>).MakeGenericType(queryableContentType);
            return queryableTypeDefinition.IsAssignableFrom(type);
        }
        return false;
    }

    public object Create(Type type)
    {
        var queryableContentType = type.GetGenericArguments()[0];
        var listType = typeof(List<>).MakeGenericType(queryableContentType);
        var list = (IEnumerable)Activator.CreateInstance(listType);
        return Queryable.AsQueryable(list);
    }

    public Priority Priority => Priority.Default;
}