SerializedDagModel.write_dag(dag)
            
            stat = DagFileStat(
                num_dags=1,
                import_errors=0,
                last_finish_time=timezone.utcnow() + timedelta(hours=1),
                last_duration=1,
                run_count=1,
            )
            manager._file_paths = [test_dag_path]
            manager._file_stats[test_dag_path] = stat
            active_dag_count = (
                session.query(func.count(DagModel.dag_id))
                .filter(DagModel.is_active, DagModel.fileloc == test_dag_path)
                .scalar()
            )
            assert active_dag_count == 1
            serialized_dag_count = (
                session.query(func.count(SerializedDagModel.dag_id))
                .filter(SerializedDagModel.fileloc == test_dag_path)
                .scalar()
            )
            assert serialized_dag_count == 1
            manager._deactivate_stale_dags()
            active_dag_count = (
                session.query(func.count(DagModel.dag_id))
                .filter(DagModel.is_active, DagModel.fileloc == test_dag_path)
                .scalar()
            )
            assert active_dag_count == 0