While becoming a Microsoft mobile beta tester is generally simple, it can require a different process depending on the platform you're on and can also vary from app to app. Android has a few different ways to become a beta tester.
Microsoft, Google Play and Android apps
There are many Microsoft Android apps that you can beta test. There are multiple ways to do so though, rather than using a unified beta testing application like on iOS.
Becoming a beta tester for Microsoft's apps on Android generally requires clicking a specific link that is usually available through a Google+ Community dedicated to each app's beta program. But Google+ is going away for consumers in April, so you can use the following links to directly become a beta tester. Additionally, some Android apps have a second listing in the Google Play Store that is the beta version of the app. Signing up for those is as easy as installing the app like any other application.
You can also become a beta tester for Microsoft Launcher by going into the app's settings menu, selecting “contact us”, and then selecting “join the beta program.”
Get to testing!
Being a beta tester is fun because you get to try out new features that Microsoft either plans to implement or is considering putting inside the standard versions of their applications. You also can help these apps' development because you can give feedback to Microsoft for any app that you test.