Rails will infer the controller you want to test from the class name of the test case. For example...

class PeopleControllerTest < ActionController::TestCase
end

will test the app/controllers/people_controller.rb.

To change this is trivial. Use the "test" method inside your test case.

class PeopleControllerImportContactsFromGmailTest < ActionController::TestCase
     tests PeopleController
end

You might want to do this to separate actions in your controller by file in your test suite.