it 'delete_all_selected_topics for a private assignment and redirects to edit assignment page with single topic selected' do
      create(:topic, id: 2, assignment_id: 2, topic_identifier: 'topic2')
      request_params = { assignment_id: 2, topic_ids: ['topic2'] }
      post :delete_all_selected_topics, params: request_params
      expect(flash[:success]).to eq('All selected topics have been deleted successfully.')