You’re welcome Raimonds!
You get the testDeviceId by inspecting the log output on your Android device. Here is a detailed explanation for it: http://stackoverflow.com/questions/4524752/how-can-i-get-device-id-for-admob
Thanks for bringing up this question – we will enhance the documentation so it will be more clear for future customers.
You are right, the hint about adding it to the config file is also missing in the docs – please make sure to add it to the config file, we’ll also add this information to the next doc version. Well spotted 😉