Once TaskGroups (https://airflow.readthedocs.io/en/latest/concepts.html#taskgroup) that would be released in Airflow 2.0 reach feature parity with SubDags and we have wide adoption and feedback from users about Taskgroups we should deprecate Subdags and remove them eventually in Airflow 3.0.

Discussion Thread: https://lists.apache.org/thread.html/ra52746f9c8274469d343b5f0251199de776e75ab75ded6830886fb6a%40%3Cdev.airflow.apache.org%3E
tests/operators/test_subdag_operator.py
"""
        Subdags and subdag tasks with no pool overlap, should not to query
        pools
        """
        dag = DAG('parent', default_args=default_args)
        subdag = DAG('parent.child', default_args=default_args)
        session = airflow.settings.Session()
        pool_1 = airflow.models.Pool(pool='test_pool_1', slots=1)
        pool_10 = airflow.models.Pool(pool='test_pool_10', slots=10)
        session.add(pool_1)
        session.add(pool_10)
        session.commit()
        DummyOperator(task_id='dummy', dag=subdag, pool='test_pool_10')
        mock_session = Mock()
        SubDagOperator(task_id='child', dag=dag, subdag=subdag, pool='test_pool_1', session=mock_session)
        assert not mock_session.query.called
        session.delete(pool_1)
        session.delete(pool_10)
        session.commit()
    def test_execute_create_dagrun_wait_until_success(self):