The test fails quite regularly - usually in one of many jobs:

Example


https://github.com/apache/airflow/pull/12850/checks?check_run_id=1506517544

```
______________ 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/jobs/test_scheduler_job.py:2415: AssertionError


```

tests/test_utils/asserts.py
stack = [
            f
            for f in traceback.extract_stack()
            if 'sqlalchemy' not in f.filename
            and __file__ != f.filename
            and ('session.py' not in f.filename and f.name != 'wrapper')
        ]
        stack_info = ">".join([f"{f.filename.rpartition('/')[-1]}:{f.name}" for f in stack][-3:])
        lineno = stack[-1].lineno
        self.result[f"{stack_info}:{lineno}"] += 1
count_queries = CountQueries  
@contextmanager
def assert_queries_count(expected_count, message_fmt=None):
    with count_queries() as result:
        yield None
    count = sum(result.values())
    if expected_count != count:
        message_fmt = (
            message_fmt
            or "The expected number of db queries is {expected_count}. "
            "The current number is {current_count}.\n\n"
            "Recorded query locations:"
        )
        message = message_fmt.format(current_count=count, expected_count=expected_count)
        for location, count in result.items():
            message += f'\n\t{location}:\t{count}'
        raise AssertionError(message)