>> "Would it make sense to create a framework that lives entirely in Cocoa and only syncs with a server? "

I haven't finished the full article yet but as the Facebook app is available on multiple platforms I'd say it wouldn't make sense to develop the testing framework in native code entirely for each platform. Look how long it took for Facebook to give up on HTML and switch their app dev to native. If possible they would probably do the testing framework non-native.