Error while accessing Flask config while testing

While writing tests for my Flask app I came across an issue when trying to set Flask config settings.

Usually, I do it like this:

import unittest

from factory import create_app


class ConfigTests(unittest.TestCase):

    def setUp(self):
        app = create_app('flask_test.cfg')
        app.testing = True
        self.app = app.test_client()

    def test_app_is_development(self):
        self.assertTrue(self.app.application.config['SECRET_KEY'] is 'secret_key')
        self.assertTrue(self.app.application.config['DEBUG'] is True)

This resulted in an error

AttributeError: 'FlaskClient' object has no attribute 'config'

Only from debugging I saw that there was no "config" attribute instead I had to go self.app.application.config to get it to work.

import unittest

from factory import create_app


class ConfigTests(unittest.TestCase):

    def setUp(self):
        app = create_app('flask_test.cfg')
        app.testing = True
        self.app = app.test_client()

    def test_app_is_development(self):
        self.assertTrue(self.app.application.config['SECRET_KEY'] is 'secret_key')
        self.assertTrue(self.app.application.config['DEBUG'] is True)

Am I doing something, did Flask change this in an update or is there a better way to do this?