Шаблоны не отображаются в модульном тесте Airflow

У меня есть модуль Python, который структурирован следующим образом:

my_module/
  ...
  tests/
    __init__.py
    my_test.py
    ...

где my_test.py определяется следующим образом:

from __future__ import print_function, unicode_literals

import os
import unittest
from datetime import timedelta, date

from airflow import configuration
from airflow.models import TaskInstance as TI, DAG, DagRun
from airflow.operators.python_operator import PythonOperator
from airflow.settings import Session
from airflow.utils import timezone
from airflow.utils.state import State

DEFAULT_DATE = timezone.datetime(2016, 1, 1)
END_DATE = timezone.datetime(2016, 1, 2)
INTERVAL = timedelta(hours=12)
FROZEN_NOW = timezone.datetime(2016, 1, 2, 12, 1, 1)

TI_CONTEXT_ENV_VARS = ['AIRFLOW_CTX_DAG_ID',
                       'AIRFLOW_CTX_TASK_ID',
                       'AIRFLOW_CTX_EXECUTION_DATE',
                       'AIRFLOW_CTX_DAG_RUN_ID']


class Call:
    def __init__(self, *args, **kwargs):
        self.args = args
        self.kwargs = kwargs


def build_recording_function(calls_collection):
    """
    We can not use a Mock instance as a PythonOperator callable function or some tests fail with a
    TypeError: Object of type Mock is not JSON serializable
    Then using this custom function recording custom Call objects for further testing
    (replacing Mock.assert_called_with assertion method)
    """
    def recording_function(*args, **kwargs):
        calls_collection.append(Call(*args, **kwargs))
    return recording_function


class PythonOperatorTest(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        super(PythonOperatorTest, cls).setUpClass()

        session = Session()

        session.query(DagRun).delete()
        session.query(TI).delete()
        session.commit()
        session.close()

    def setUp(self):
        super(PythonOperatorTest, self).setUp()
        configuration.load_test_config()
        self.dag = DAG(
            'test_dag',
            default_args = {
                'owner': 'airflow',
                'start_date': DEFAULT_DATE},
            schedule_interval=INTERVAL)
        self.addCleanup(self.dag.clear)
        self.clear_run()
        self.addCleanup(self.clear_run)

    def tearDown(self):
        super(PythonOperatorTest, self).tearDown()

        session = Session()

        session.query(DagRun).delete()
        session.query(TI).delete()
        print(len(session.query(DagRun).all()))
        session.commit()
        session.close()

        for var in TI_CONTEXT_ENV_VARS:
            if var in os.environ:
                del os.environ[var]

    def do_run(self):
        self.run = True

    def clear_run(self):
        self.run = False

    def is_run(self):
        return self.run

    def _assertCallsEqual(self, first, second):
        self.assertIsInstance(first, Call)
        self.assertIsInstance(second, Call)
        self.assertTupleEqual(first.args, second.args)
        self.assertDictEqual(first.kwargs, second.kwargs)

    def test_python_callable_arguments_are_templatized(self):
        """Test PythonOperator op_args are templatized"""
        recorded_calls = []

        task = PythonOperator(
            task_id='python_operator',
            # a Mock instance cannot be used as a callable function or test fails with a
            # TypeError: Object of type Mock is not JSON serializable
            python_callable=(build_recording_function(recorded_calls)),
            op_args=[
                4,
                date(2019, 1, 1),
                "dag {{dag.dag_id}} ran on {{ds}}."
            ],
            dag=self.dag)

        self.dag.create_dagrun(
            run_id='manual__' + DEFAULT_DATE.isoformat(),
            execution_date=DEFAULT_DATE,
            start_date=DEFAULT_DATE,
            state=State.RUNNING
        )
        task.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE)

        self.assertEqual(1, len(recorded_calls))
        self._assertCallsEqual(
            recorded_calls[0],
            Call(4,
                 date(2019, 1, 1),
                 "dag {} ran on {}.".format(self.dag.dag_id, DEFAULT_DATE.date().isoformat()))
        )

В терминале, когда я запускаю nosetests test/my_test.py, тест не проходит, потому что шаблоны Jinja отображаются неправильно. Полный журнал приведен ниже.

======================================================================
FAIL: Test PythonOperator op_args are templatized
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/user/my_module/tests/my_test.py", line 120, in test_python_callable_arguments_are_templatized
    "dag {} ran on {}.".format(self.dag.dag_id, DEFAULT_DATE.date().isoformat()))
  File "/home/user/my_module/tests/my_test.py", line 88, in _assertCallsEqual
    self.assertTupleEqual(first.args, second.args)
AssertionError: Tuples differ: (4, datetime.date(2019, 1, 1), 'dag {{dag.dag_id}} ran on {{ds}}.') != (4, datetime.date(2019, 1, 1), 'dag test_dag ran on 2016-01-01.')

First differing element 2:
'dag {{dag.dag_id}} ran on {{ds}}.'
'dag test_dag ran on 2016-01-01.'

- (4, datetime.date(2019, 1, 1), 'dag {{dag.dag_id}} ran on {{ds}}.')
?                                     ^^   ---------        ^^^^^^

+ (4, datetime.date(2019, 1, 1), 'dag test_dag ran on 2016-01-01.')
?                                     ^^^^^           ^^^^^^^^^^

-------------------- >> begin captured logging << --------------------
airflow.utils.log.logging_mixin.LoggingMixin: INFO: Reading the config from /home/user/airflow/airflow.cfg
airflow.settings: INFO: Configured default timezone <Timezone [UTC]>
airflow.logging_config: DEBUG: Unable to load custom logging, using default config instead
--------------------- >> end captured logging << ---------------------

Однако в коде в my_test.py нет ничего плохого, так как это всего лишь подмножество файла test_python_operator.py из файла GitHub-репозиторий воздушного потока (ветвь v1-10-stable). Наивно я ожидал, что этот тест будет работать нормально, но это не так.

What am I missing ?

РЕДАКТИРОВАТЬ: Я использую apache-airflow 1.10.2, Python 3.6.8 и Nose 1.3.7.