One other suggestion about this: `to_s` has the problem that it is both a class and an instance method of `Object`, and thus allowed the `method_defined?` confusion I commented on above.  I think it would be better to use a method that is only a class method or only an instance method so that the implementation can't be allowed to do the wrong thing.  It might be good to use the `LoadedClass` class definition from `verifying_doubles_spec.rb` since it has some stuff designed for testing this.  In fact, it might be appropriate to move these specs there since this is really an extension of that feature.