Retrieving a user’s Facebook friends will return only the subset of friends that also have the app. If your test user doesn’t have Facebook friends that have connected to your app, the list will be empty.
To get the friends, you will need to use the Facebook OAUTH which will ask the user for access to your friends (or whatever else you ask for in terms of scope).
You can then use the Facebook Graph API to grab this. There is a plugin I would think.