Question

I need to unit test a method that returns a type I can’t easily fake or instantiate. The type implements IQueryable<T> which I originally thought I could use to my advantage, but I don’t see how at this point.

For example:

public sealed class MyTrickyClass<T> : IQueryable<T>
{
    ...
}

public MyTrickyClass<T> GetData()
{
    return repository.GetAllData();
}

and my unit test

[Test Method]
public void CanGetData()
{
    var data = (new List<Record>() { new Record() }).AsQueryable();
    var mockRepository = new Mock<IRepository<Record>>();
    mockRepository.Setup(s => s.GetAllData()).Returns(data);

    MyService service = new MyService(mockRepository.Object);
    var result = service.GetData();

    Assert.IsNotNull(result);

}

This won’t compile because the return type of GetAllData() is MyTrickyClass<T>. If I try to cast data to a MyTrickyClass<Record> type, the cast fails.

All this makes sense, but it leaves me wondering what the right solution is. What are some workarounds for this kind of situation? I may be able to change the MyTrickyClass, but ideally I’d like to find a solution that leaves it alone.

Answer 1

You could have MyTrickyClass<T> implement interface ITrickyClass<T>, which inherits from IQueryable<T>. That seems minimally invasive to your class itself, and you’d have a good seam for mocking.