I want my iOS app to check if there is an update available for it on the app store

I know I can use iTunes lookup from Unity to get information about any apps already on the app store, but mine hasn't been released yet. There's a way of using a sandbox version of an app to test achievements, leaderboards, etc. Is there something similar that I can use to test checking for app updates on an app not yet in the store, or will I have to wait until it's released to find out if it works?