Application does not contain Google-Services.json, you should to create your own:
- Change application Package ID inside AndroidManifest file from "com.test.pushapp" to yours one
- Complete registration on Firebase Console and create your project there
- Go to "Project settings -> General" and add your application Package ID there
- Download "google-services.json" file and add it into project
- Change its "Build Action" from "None" to "GoogleServicesJson"
- Build and run the project
More detailed information about Firebase SDK setup you could find on official firebase documentation page.