contact.cfg has a contact named test.
contactgroups.cfg has a group named test_admins and user test is a member of that group.
services.cfg has services with contactgroup test_admins defined as the contact_group.
When user test logs in, he/she only sees those services for which the service has a contactgroup of "test_admins" defined.
Remember, you actually have to be using authentication and actually log in correctly. Which I suspect, you are NOT doing.