iOS In App Purchase: test a real purchase without submitting to Apple
You can actually test the in-app purchasing in the sandbox environment, basically you'll need to set up an test user account in your iTunesConnect.
Check the apple documentation here:http://developer.apple.com/library/ios/#technotes/tn2259/_index.html
You'll be able to find all the information related to In-App Purchasing, including sandbox testing.
Short answer: you can't test a real purchase (aka, spend real money). It isn't possible.
Slightly longer answer: You'll automatically hit the sandbox environment unless it's an apple-signed release build. Even ad-hoc signed builds hit the sandbox.
To test a new IAP: create your IAP (it will be in "needs approval mode" until submitted with the final build and test against the sandbox - that's fine). If your purchase works against the sandbox, it should work against prod with real money as well. It would be great to do a trial run with real money, but that's just not possible until the IAP is approved and you get the production signed version of the app from the app store.