@snazy do you mind if I borrow your commit and only keep the tests?

@snazy do you mind if I borrow your commit and only keep the tests?

Sure! Take that one :)

I suspect, this change also needs a custom converter for Map?

Done, PR updated

Thanks again for the idea! It was marvelously simple and effective

I suppose we are ok with loosing the immutable semantics?

That would only be a problem if folks where actually adding information into the parameters in the test methods.
I don't think it's something we have to worry about in this case

I also do think making it work in general is more important than retaining immutability.

It's for the test method(s) parameters, so I doubt that immutability matters (a lot).

Yeah, I think we are fine losing immutability for that. That's why I suggested this approach.
Worst case, you can wrap these in a Collections.toUnmodifiable... if these are supported by XStream.