Google has no helpful documentation on how to clear test purchases you’ve made on your device with a Alpha/Beta build.  If I clear the App’s local cache, and re-run it, then it just automatically remakes the purchases (which is a good thing – no restore purchase option required).

I found this on StackOverflow, and posted it here as a reminder to myself:

adb shell pm clear com.android.vending

Does the trick – remember to clear the App’s cached data store too.