Facebook now allows using Graph API to create and manage test accounts. "You can create up to 50 test users per app and define specific permissions for each user. The creation API returns a login_url and access token, which allows you to easily sign in as the test user for manual testing or use the access token for automated testing."
Creating a test user using Graph API: POST /app_id/accounts/test-users?installed=true&permissions=read_stream
In addition, you can easily generate friend connections between test users of same app via API to test interactions between users.
Generate friend request: POST /test_user_id_1/friends/test_user_id_2
Accept friend request: POST /test_user_id_2/friends/test_user_id_1
"This system is designed to let you to test your app in either live mode or sandbox mode. These test users cann't interact with real users, so they don't need to be verified and their activity isn't monitored by our spam detection systems," stated Facebook.
More Info: documentation page