The testing process is cumbersome.
For Apple:
You have to have designated test accounts with their own Apple ID’s. Each account can only make a non-consumable purchase once. I believe Apple has test products that you can buy over and over, but that doesn’t necessarily help you verify you’re setup is good. Also there are ever changing requirements on what has to be submitted and when.
For Google, you cannot use your developer account to do purchases, even in testing, so you will also need another Google Mail account to test your IAP. Google for certain has a series of test products you can use while testing your code. But unlike Apple, you can refund your non-consumable purchases and try the again (albeit that’s a pain to do). Google just needs an Alpha or Beta build published to Google Play, no odd submissions of your products or any thing.
I’ll see what I can do about getting the IAP guide up soon.
Rob