That's true. I think this test is outdated. It was originally added here: https://github.com/rails/rails/commit/786342e17f42799ef889cf6127fe97e9598272e0. Which brings me to a second discussion, should we be raising an ArgumentError when the input is not a hash?

It seems like this second check will ensure that all arguments are correct and valid, and that ``stringify_keys`` will never throw a NoMethodError if we are sure that a ``new_attributes`` is a hash.