Getting "test user" alert

getting “test user” alert. getting random alert like below image on first time app open. does anyone know reason of this?

First things first, who wrote or created or developed the app?

i have made app in ionic3. but i was getting this type of alert on first time open of an app.
i have fixed this issue by downgrading version of “cordova-plugin-firebasex” from 11.0.3 to 9.1.2-cli. but i could not found reason that why this type of alert coming in latest version of “cordova-plugin-firebasex”!

check on initializeApp()
send code initializeApp() here