refactoring setup_roles and updated tests

spec/models/conference_spec.rb

@@ -52,6 +52,11 @@ describe Conference do
 
   describe '#user_registered?' do
 
+    # It is necessary to use bang version of let to build roles before user
+    let!(:organizer_role) { create(:organizer_role) }
+    let!(:participant_role) { create(:participant_role) }
+    let!(:admin_role) { create(:admin_role) }
+
     let(:user) { create(:user) }
 
     context 'user not registered' do