It's not too hard to beta test an Android app, but the process still tends to involve jumping through a few hoops. You might need to visit the developer's website, for instance, or join a community.
Google is rolling out a Play Store update that lets you join or leave Android betas right from the regular app's listing. Certain tests may ask you to sign up for a Google+ community first, but you won't have to go scrounging for a beta-specific app entry or download an installer from a website.
The updated store will also let you know when you're using a beta-only app (that is, there has never been a finished release). And you're not writing regular reviews anymore -- instead, you're leaving private feedback for the developer.