I\'ve looked on SO at a lot of questions regarding this, and they all seem to say that if the app is a paid app, then Alpha and Beta testers will also have to pay to test it
The answer is that, yes, you can allow beta testers to test a paid app without paying, but it requires you to create a new Promo in the Developer Console, with one promo code for each beta tester.
So if, for example, you expect to have not more than 10 beta testers that you will ask to test your app (without paying for it), then you would create a new promo with 10 codes, and provide one code to each of your testers.
Don't forget to include a code for yourself, too, so you can install the program/test it on your own device for free (without having to do so via ADB).
There is now an alternative to doing this without generating promo codes. However it does give the testers access to all apps distributed by your developer account.
Go to the Google Play Console where you see the list of all of your apps. On the left go to Settings. Under "License Testing" enter the accounts that you want to have access. This will also allow those accounts to test IAPs.