I'm with you 100% re: constructors not having side effects, but that also extends to all behaviors of any class, right? Otherwise it could be said that a class isn't the right tool for this task—will a suite ever need more then one instance of MocksHelper? I suspect it's possible. The purpose of the class itself is to initialize some list of mocks on window object and do the set up and teardown, right? If the purpose is always to do some operation that will have side-effects, then I think its ok to simplify where the side effects themselves actually occur.

Anyway, that's all meta-program semantics discussion and I follow your rationale :)