What I want? After retrieving all purchased items I need to verify the purchase on my server, this I want to do with the signature and signed data received from the in-app payme
You no longer get signatures for test purchases (android.test.*). I took the dive and uploaded my app to the market place (just didn't publish it) using my real products.
Low and behold signatures started to be returned! I recommend amending any server side validation you are using to skip the signature check when the data contains an android.test.* item id.
Note: The important bit about the above is: "using my real products".