How to test a Connexion/Flask app?

I'm using the Connexion framework for Flask to build a microservice. I would like to write tests for my application using py.test.

In the pytest-flask doc it says to create a fixture in conftest.py that creates the app like so:

conftest.py

import pytest

from api.main import create_app


@pytest.fixture
def app():
    app = create_app()
    return app

In my test I'm using the client fixture like this:

test_api.py

def test_api_ping(client):
    res = client.get('/status')
    assert res.status == 200

However when I run py.test I get the following error message:

==================================== ERRORS ====================================
_______________________ ERROR at setup of test_api_ping ________________________

request = <SubRequest '_monkeypatch_response_class' for <Function 'test_api_ping'>>
monkeypatch = <_pytest.monkeypatch.MonkeyPatch instance at 0x7f9f76b76518>

    @pytest.fixture(autouse=True)
    def _monkeypatch_response_class(request, monkeypatch):
        """Set custom response class before test suite and restore the original
        after. Custom response has `json` property to easily test JSON responses::

            @app.route('/ping')
            def ping():
                return jsonify(ping='pong')

            def test_json(client):
                res = client.get(url_for('ping'))
                assert res.json == {'ping': 'pong'}

        """
        if 'app' not in request.fixturenames:
            return

        app = request.getfuncargvalue('app')
        monkeypatch.setattr(app, 'response_class',
>                           _make_test_response_class(app.response_class))
E       AttributeError: 'App' object has no attribute 'response_class'

How can I make py.test work? Here is my create_app function:

main.py

import connexion


def create_app():
    app = connexion.App(__name__, port=8002,)
    app.add_api('swagger.yaml')
    return app


if __name__ == "__main__":
    create_app().run()