What about \"Paid Apps\" as Alpha/Beta testing...
I am uploading one \"alpha_version\" apk under \"Alpha\" tab... I have tagged application as \"Paid\"
If you want users to test your app for free in the Play store and sell your app to the general public, then you could distribute your app in an obfuscated name with irrelevant description for free for testers, and the real app, with the real name/description etc will be paid
Please see my answer here: https://stackoverflow.com/a/35352421/5916188
Yes, you can use a promo code to give beta testers (and others) a free copy at install time.
It's annoying but you could just create another app in your developer console that is free and load your APK there. You will have to change the package name though and maybe give it a test name. Keep this free app in beta and then they can test it for free.
Then when you want to release it you create a new app that is paid and release that.