Generate URLs for Flask test client with url_for function

Question

I'm trying to write unit tests for a Flask app using pytest. I have an app factory:

def create_app():
    from flask import Flask
    app = Flask(__name__)
    app.config.from_object('config')
    import os
    app.secret_key = os.urandom(24)
    from models import db
    db.init_app(app)
    return app

And a test class:

class TestViews(object):

    @classmethod
    def setup_class(cls):
        cls.app = create_app()
        cls.app.testing = True
        cls.client = cls.app.test_client()

    @classmethod
    def teardown_class(cls):
        cls.app_context.pop()

    def test_create_user(self):
        """
        Tests the creation of a new user.
        """
        view = TestViews.client.get(url_for('create_users')).status_code == 200

but when I run my tests I get the following error:

RuntimeError: Attempted to generate a URL without the application context being pushed. This has to be executed when application context is available.

Googling this tells me (I think) that using the test client should create an automatic application context. What am I missing?

Answer 1

Making requests with the test client does indeed push an app context (indirectly). However, you're confusing the fact that url_for is visually inside the test request call with the idea that it is actually called inside. The url_for call is evaluated first, the result is passed to client.get.

url_for is typically for generating URLs within the app, unit tests are external. Typically, you just write exactly the URL you're trying to test in the request instead of generating it.

self.client.get('/users/create')

If you really want to use url_for here, you must do it in an app context. Note that when you're in an app context but not a request context, you must set the SERVER_NAME config and also pass _external=False. But again, you should probably just write out the URL you're trying to test.

app.config['SERVER_NAME'] = 'localhost'

with self.app.app_context():
    url = url_for(..., _external=False)

self.client.get(url, ...)