Apple's new TestFlight service is a great way to test software and installing a beta couldn't be easier.
A while back Marco Arment was looking for beta testers for Overcast so he could finetune his new sync engine. As an avid podcast listener I enrolled and every couple of days a new build of Overcast became available via TestFlight.
But yesterday after Marco Arment's latest Overcast release was finally approved, the update didn't show up in the App Store for me. Since betas (probably) have the same build number as the update that's been approved, you're not automatically updated once the update becomes available in the App Store.
TestFlight betas only work for 30 days, after which they're deactivated or replaced with a more recent build. Which means that, if Marco doesn't update the Testflight beta within 30 days, Overcast will stop working if I keep the beta on my device.
Not wanting to delete the app and reinstall the App Store version from scratch (and losing all downloaded data in the process) I started searching Apple's website for a solution, but alas nothing's there about this issue.
In the end the solution is easy: open the App Store, search for the App. It'll show up with a download button and it'll install right over the beta version with no data loss.
It's obvious once you know it.