How to tell at runtime whether an iOS app is running through a TestFlight Beta install

For an application installed through TestFlight Beta the receipt file is named StoreKit/sandboxReceipt vs the usual StoreKit/receipt. Using [NSBundle appStoreReceiptURL] you can look for sandboxReceipt at the end of the URL.

NSURL *receiptURL = [[NSBundle mainBundle] appStoreReceiptURL];
NSString *receiptURLString = [receiptURL path];
BOOL isRunningTestFlightBeta =  ([receiptURLString rangeOfString:@"sandboxReceipt"].location != NSNotFound);

Note that sandboxReceipt is also the name of the receipt file when running builds locally and for builds run in the simulator.

Swift Version:

let isTestFlight = Bundle.main.appStoreReceiptURL?.lastPathComponent == "sandboxReceipt"