I recently got to know this code "*#0*#" when I was searching the internet. If you're Samsung Galaxy user, you can simply run code by dialling it regular dialling screen. I tried it on my Samsung Galaxy Grand Prime device. Once this code is dialled, the device shows you a screen with various options. You can check if the option is working well using this screen. I myself tapped on "Speaker" option and a song was played by the device to check the speaker was working fine.I hope this will be useful for you