With this app you can easly figure out which key codes represent which key on your bluetooth gamepad on your android game built in Unity. As well it can be used to test a gamepad connected on your android device.

How to use it for development in Unity

Connect a controller through bluetooth or OTG, then open the app and try to press buttons on your controller, the app gonna show on each button press which key code represent the button you pressing in a form of unity keycode e.g "joystick 1 button 0" it can log as well all the analog axis (max 6).
You can aswell see on button press which key visualy represent on an xbox controller (xInput) the button you just pressed.

You can use it as well to test a gamepad in general.