Source of the Demo App found on Google Play to check whether Push Notifications can be received (http://firebase.google.com/docs/cloud-messaging/)

Reuse the same Firebase project you've used for the server part (https://github.com/berndfinal/PushNotificationTester_Web). In the Firebase Console go to Project Settings, add your Android App and download the generated google-services.json file. Copy it into the app folder

Deploy the server part on Google App Engine and modify the URL's in ConnectThread and TriggerNotificationThread and you should be able to run this demo App.