If you're a developer working on an Actions on Google service or you're a maker of a smart home device or connected gadget and would like to try out your new Assistant action in different scenarios, you're a little limited for options. You likely will have to test it internally among your team, if you have one, but beyond that, you can't account for every situation and bug and will have to deploy at some point and hope things don't go wrong when many people start using it. But now you can test it out, as you would an Android app.
The Actions on Google team is rolling out alpha and beta testing ability to developers, so they can select a number of users and send them their actions or updates to existing actions for testing before releasing them to the public. That should help ensure most of the bugs are ironed out and the different situations are accounted for prior to release.
If you're a user, you will get an invitation link from the developer to become a tester - same wording as the Play Store. Once you approve, you can still change which channel you're in by going to Assistant's settings, tapping on Services (it isn't live yet), choosing the action you're testing in the list, and selecting whether you want to be on "no testing," "alpha testing," or "beta testing."
- Google Assistant