Contrary to many answers and comments on SO and other sites, you do NOT have to perform preliminary tests with an alpha/beta version of your product that has been downloaded from Google Play onto your test device (the alpha/beta publication process often eats up half a day). Neither do you have to load and re-load a signed release apk from your developer studio to your test device.
You CAN debug preliminary Google Play in app billing services using the debug app as loaded from your developer studio directly to your test device via ADB. If you are experiencing errors that prevent this, likely you have done something wrong in your code. Pay especially close attention to the CASE of your SKU's (product ids) and their format (for example, if you load your APK as com.mydomain.my_product_id, be sure your try to purchase it this way - providing the same case and domain). Also, pay especially close attention to your itemType - this should be either "inapp" or "subs" for managed/unmanaged in app purchases or subscriptions, respectively.
As suggested by Chirag Patel, provided you have your billing code properly established, perform all testing using the android.test.purchased Sku (product ID) during your preliminary tests. Check for this ID throughout your billing operations to pass it through signature, token and payload checks, since this data is not provided by the Google test system. Additionally, give one of your test products this ID to test its purchase, unlock/load and presentation all the way through your schema. To CLEAR the purchase, simply consume it, passing the same Sku AND a token string formatted this way - no other fields are relevant :
"inapp:"+appContext.getAppContext().getPackageName()+":android.test.purchased";
Once you have completed this phase of testing, move to semi-live testing with your alpha/beta product. Create a Google group (essentially a mailing list), add your test users emails to it, and add/invite this group to test your device in this phase (performed at the "APK" portion of your app's Google developer listing). Purchases will be simulated but not actually charged - however to clear and re-test the purchases, Google indicates that you must refund them from your Google wallet. THIS is the only phase of testing that requires the time-consuming process of using alpha/beta loads and test users.