I'm not sure disabling monkeypatching would suffice, couldn't you then just create your own type equal to everything and return that? I assume assert_equal just does `a == b` internally so `a` could be an AlwaysEqual instance rather than a monkeypatched nil.

A more sensible alternative would probably be to serialise the assert_equal parameters and check the results externally.

Adding negative tests (using `not a == b` to avoid the same monkeypatching of !=) would also help

They could just add a test that makes sure trivial comparisons still work.

you mean sandbox the interpreter that the kata runs in? Extract the value and then de-serialise it for an equality check in another instance of the interpreter?