How to test session in flask resource
Question: I'd like to test a resource. The response of that depends on a parameter in
session (logged) To test this resource, I've wrote those tests:

    
    
    import app
    import unittest
    
    class Test(unittest.TestCase):
        def setUp(self):
            self.app = app.app.test_client()
    
        def test_without_session(self):
            resp = self.app.get('/')
            self.assertEqual('without session', resp.data)
    
        def test_with_session(self):
            with self.app as c:
                with c.session_transaction() as sess:
                    sess['logged'] = True
                resp = c.get('/')
            self.assertEqual('with session', resp.data)
    
    
    if __name__ == '__main__':
        unittest.main()
    

My app.py is this:

    
    
    from flask import Flask, session
    
    
    app = Flask(__name__)
    
    
    @app.route('/')
    def home():
        if 'logged' in session:
            return 'with session'
        return 'without session'
    
    
    if __name__ == '__main__':
        app.run(debug=True)
    

When i run the tests I have this error:

    
    
    ERROR: test_pippo_with_session (__main__.Test)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "test_pippo.py", line 17, in test_pippo_with_session
        with c.session_transaction() as sess:
      File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
        return self.gen.next()
      File "/home/tommaso/repos/prova-flask/local/lib/python2.7/site-packages/flask/testing.py", line 74, in session_transaction
        raise RuntimeError('Session backend did not open a session. '
    RuntimeError: Session backend did not open a session. Check the configuration
    

I haven't found any solution on google.


Answer: If you did not set a custom `app.session_interface`, then you forgot to set a
[secret
key](https://flask.readthedocs.org/en/latest/api/?highlight=session#flask.Flask.secret_key):

    
    
    def setUp(self):
        app.config['SECRET_KEY'] = 'sekrit!'
        self.app = app.app.test_client()
    

This just sets a mock secret key for the tests, but for your application to
work you'll need to generate a production secret key, see the [sessions
section in the Quickstart
documentation](https://flask.readthedocs.org/en/latest/quickstart/#sessions)
for tips on how to produce a good secret key.

Without a secret key, the default [session
implementation](https://flask.readthedocs.org/en/latest/api/?highlight=session#flask.sessions.SecureCookieSessionInterface)
fails to create a session.

