How to test code changes before updating an app in App Store
When you have an app in the App Store and are making an updates to the same, when it comes to test how an upgraded app will behave, Apple recommends:
Install an ad hoc distribution of an archived build of the update using iTunes on a device that already has the old version of the app installed.
In other words, don’t use Xcode to install/run your updated code tests. Reason being, Xcode pushes only changed files, which makes for a faster build process.
And in turn:
…using Xcode to install an app over an older old build can make a “frankenbuild” with legacy files it wouldn’t otherwise have. This can cause problems during testing and mask bugs.