After some research I came to the following conclusion.
Before version 5, the library worked fine using android.test.purchased.
Without having any Apk inserted on the store the result was the following:
From version 5 of the library (this is not only for B4X but for all) it is not possible to use this test.
If placed on the store as a definitive version everything works, but unfortunately it is not possible to run the test only with the apk as happened before Rel. 5 of the billing library.
Following several links where they expose the same problem
I'm using wrapper for BillingClient and after migration from Billing Library 4.0 to 5.0 there is an issue with unit testing of specific builder - BillingFlowParams.SubscriptionUpdateParams builder.
This is entirely untested and slapped together, but is an example of how it could be handled: using System; using System.Reflection; using System.Diagnostics; using System.Threading.Tasks; using System.Linq; using System.Collections.Generic; using Plugin.InAppBilling; public class DlcManager...
What can i say, let's hope Google fixes this bug soon. (maybe already from Rel. 6.00).