Accessing Flask test client session in pytest test when using an app factory

I'm trying to unittest an application using pytest and an app factory, but I can't seem to get access to the client session object in my tests. I'm sure there's some context I'm not pushing somewhere. I push the app context in my 'app' fixture. Should I push the request context somewhere?

The following is an MWE.

mwe.py:

from flask import Flask, session


def create_app():
    app = Flask(__name__)
    app.secret_key = 'top secret'

    @app.route('/set')
    def session_set():
        session['key'] = 'value'
        return 'Set'

    @app.route('/check')
    def session_check():
        return str('key' in session)

    @app.route('/clear')
    def session_clear():
        session.pop('key', None)
        return 'Cleared'

    return app


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

conftest.py:

import pytest
from mwe import create_app


@pytest.fixture(scope='session')
def app(request):
    app = create_app()

    ctx = app.app_context()
    ctx.push()

    def teardown():
        ctx.pop()

    request.addfinalizer(teardown)
    return app


@pytest.fixture(scope='function')
def client(app):
    return app.test_client()

test_session.py:

import pytest
from flask import session


def test_value_set_for_client_request(client):  # PASS
    client.get('/set')
    r = client.get('/check')
    assert 'True' in r.data


def test_value_set_in_session(client):  # FAIL
    client.get('/set')
    assert 'key' in session


def test_value_set_in_session_transaction(client):  # FAIL
    with client.session_transaction() as sess:
        client.get('/set')
        assert 'key' in sess

Note that running this directly works fine, I can jump around /set, /check, /clear and it behaves as expected. Similarly, the test that uses only the test client to GET the pages works as expected. Accessing the session directly however doesn't seem to.