Testing Flask login and authentication?

Question

I'm developing a Flask application and using Flask-security for user authentication (which in turn uses Flask-login underneath).

I have a route which requires authentication, /user. I'm trying to write a unit test which tests that, for an authenticated user, this returns the appropriate response.

In my unittest I'm creating a user and logging as that user like so:

from unittest import TestCase
from app import app, db
from models import User
from flask_security.utils import login_user

class UserTest(TestCase):
   def setUp(self):
       self.app = app
       self.client = self.app.test_client()
       self._ctx = self.app.test_request_context()
       self._ctx.push()

       db.create_all()

   def tearDown(self):
       if self._ctx is not None:
           self._ctx.pop()

       db.session.remove()
       db.drop_all()

   def test_user_authentication():
       # (the test case is within a test request context)
       user = User(active=True)
       db.session.add(user)
       db.session.commit()
       login_user(user)

       # current_user here is the user
       print(current_user)

       # current_user within this request is an anonymous user
       r = test_client.get('/user')

Within the test current_user returns the correct user. However, the requested view always returns an AnonymousUser as the current_user.

The /user route is defined as:

class CurrentUser(Resource):
    def get(self):
        return current_user  # returns an AnonymousUser

I'm fairly certain I'm just not fully understanding how testing Flask request contexts work. I've read this Flask Request Context documentation a bunch but am still not understanding how to approach this particular unit test.

Answer 1

The problem are different request contexts.

In your normal Flask application, each request creates a new context which will be reused through the whole chain until creating the final response and sending it back to the browser.

When you create and run Flask tests and execute a request (e.g. self.client.post(...)) the context is discarded after receiving the response. Therefore, the current_user is always an AnonymousUser.

To fix this, we have to tell Flask to reuse the same context for the whole test. You can do that by simply wrapping your code with:

with self.client:

You can read more about this topic in the following wonderful article: https://realpython.com/blog/python/python-web-applications-with-flask-part-iii/

Example

Before:

def test_that_something_works():
    response = self.client.post('login', { username: 'James', password: '007' })

    # this will fail, because current_user is an AnonymousUser
    assertEquals(current_user.username, 'James')

After:

def test_that_something_works():
    with self.client:
        response = self.client.post('login', { username: 'James', password: '007' })

        # success
        assertEquals(current_user.username, 'James')

Answer 2

The problem is that the test_client.get() call causes a new request context to be pushed, so the one you pushed in your the setUp() method of your test case is not the one that the /user handler sees.

I think the approach shown in the Logging In and Out and Test Adding Messages sections of the documentation is the best approach for testing logins. The idea is to send the login request through the application, like a regular client would. This will take care of registering the logged in user in the user session of the test client.

Answer 3

I didn't much like the other solution shown, mainly because you have to keep your password in a unit test file (and I'm using Flask-LDAP-Login, so it's nonobvious to add a dummy user, etc.), so I hacked around it:

In the place where I set up my test app, I added:

@app.route('/auto_login')
def auto_login():
    user = ( models.User
             .query
             .filter_by(username="Test User")
             .first() )
    login_user(user, remember=True)
    return "ok"

However, I am making quite a lot of changes to the test instance of the flask app, like using a different DB, where I construct it, so adding a route doesn't make the code noticeably messier. Obv this route doesn't exist in the real app.

Then I do:

def login(self):
    response = self.app.test_client.get("/auto_login")

Anything done after that with test_client should be logged in.