This is one of the most frequently asked question by most of the Windows Phone developers or some one who is getting started with the Windows Phone development .
How to test a Windows Phone 8 app on device ?
To test a Windows Phone 8 app on a device , you just need a Microsoft account which one can use to register the phone to test the app on it.
A developer account is now optional . Simply , a Microsoft account (live id) is more than enough for testing the app on device .
If you have a valid developer account , you can have up to 3 devices to be developer unlocked for app development and testing before you can publish it to the Windows Phone store .
In case , you don’t have a developer account , you can use the Microsoft account / live id to register only one device and use it for testing the app.