`ArgumentError` is prone to false positives because ruby itself raises it when you call a method with invalid args, so there could be something in the rspec-mocks implementation code that is calling one of its methods wrongly and causing `ArgumentError` to be raised.  It would be good to specify something about the message to ensure it's the desired argument error and not and accidental one from a refactoring that left an extra arg in a method call or whatever.