We have flaky scheduler test:


https://github.com/apache/airflow/pull/11659/checks?check_run_id=1279791496#step:6:527


_______________ TestSchedulerJob.test_scheduler_task_start_date ________________

self = <tests.jobs.test_scheduler_job.TestSchedulerJob testMethod=test_scheduler_task_start_date>

    def test_scheduler_task_start_date(self):
        """
        Test that the scheduler respects task start dates that are different from DAG start dates
        """
    
        dagbag = DagBag(dag_folder=os.path.join(settings.DAGS_FOLDER, "no_dags.py"), include_examples=False)
        dag_id = 'test_task_start_date_scheduling'
        dag = self.dagbag.get_dag(dag_id)
        dag.is_paused_upon_creation = False
        dagbag.bag_dag(dag=dag, root_dag=dag)
    
        # Deactivate other dags in this file so the scheduler doesn't waste time processing them
        other_dag = self.dagbag.get_dag('test_start_date_scheduling')
        other_dag.is_paused_upon_creation = True
        dagbag.bag_dag(dag=other_dag, root_dag=other_dag)
    
        dagbag.sync_to_db()
    
        scheduler = SchedulerJob(executor=self.null_exec,
                                 subdir=dag.fileloc,
                                 num_runs=2)
        scheduler.run()
    
        session = settings.Session()
        tiq = session.query(TaskInstance).filter(TaskInstance.dag_id == dag_id)
        ti1s = tiq.filter(TaskInstance.task_id == 'dummy1').all()
        ti2s = tiq.filter(TaskInstance.task_id == 'dummy2').all()
        self.assertEqual(len(ti1s), 0)
>       self.assertEqual(len(ti2s), 2)
E       AssertionError: 1 != 2
tests/models/test_taskinstance.py
{'A': State.SUCCESS, 'B': State.NONE, 'C': State.NONE, 'D': State.NONE},
                None,
                "D -> C -> B & A -> B, when A runs but C isn't QUEUED yet, B shouldn't be QUEUED.",
            ),
            (
                {('scheduler', 'schedule_after_task_execution'): 'True'},
                {'A': 'C', 'B': 'C'},
                {'A': State.QUEUED, 'B': State.FAILED, 'C': State.NONE},
                {'A': State.SUCCESS, 'B': State.FAILED, 'C': State.UPSTREAM_FAILED},
                None,
                "A -> C & B -> C, when A is QUEUED but B has FAILED, C is marked UPSTREAM_FAILED.",
            ),
        ]
    )
    def test_fast_follow(
        self, conf, dependencies, init_state, first_run_state, second_run_state, error_message
    ):
        with conf_vars(conf):
            session = settings.Session()
            dag = DAG('test_dagrun_fast_follow', start_date=DEFAULT_DATE)
            dag_model = DagModel(
                dag_id=dag.dag_id,
                next_dagrun=dag.start_date,
                is_active=True,
            )
            session.add(dag_model)
            session.flush()
            python_callable = lambda: True
            with dag:
                task_a = PythonOperator(task_id='A', python_callable=python_callable)