Fakes should return real List implementations for .NET list types instead of a fake that is empty

[philippdolder]

No description provided.

[patrik-hagne]

Not sure I understand this one, an example?

[philippdolder]

assuming:
public interface IInterface
{
IList Items { get; }
}

The following:
var fake = A.Fake();
fake.Items.Add("item");
should lead to fake.Items containing "item".

The thing I am not sure about is if this would be a breaking change. I think it is not.

If it makes sense to you I will implement it

[patrik-hagne]

It would be a breaking change and to me it would be unsuspected behaviour. Consider this:

var fake = A.Fake<IInterface>();
A.CallTo(() => fake.Items.Add(A._)).Throws(new Exception());

That wouldn't be possible if we did return a list.

I can't think of a real use case where this is beneficial. That something is exposed as IList<T> does in no way imply that the List<T> will be used. The behaviour of the Add-method may very well vary between implementors.

Maybe I'm missing a use case here?

[philippdolder]

That's true, that's a breaking change for that case.
I didn't have your example in any case yet.

The style I do TDD I would never have such a setup that's why I didn't have your use case in mind.

While thinking about it I come to the same conclusion. The things I had in mind are no real world use cases I would have. If any pop up again, I will rethink it and come up with a solution that has no breaking changes.