Until june 20th 2016 i was able to cancel test purchases done in my app. Doing multiple in-app purchases (not consumable) from the same test account made it easy to develop
I went into the main Google Play Console page and clicked on Order Management. Under that I was able to select all test purchases and Refund them. I'm the primary developer of the app so I have access. If you are a tester you'd probably have to contact the support team and request that they refund your order.