Unit test a Flask session - cannot reproduce failure with session_transaction

Question

I am testing a Flask application (Flask 0.9), and in particular I have a session fixture that I would like to run in the documented-way, being something like this (as I understand it):

from flask import Flask, session
app = Flask(__name__)

@app.route('/', methods=['POST'])
def m():
    logging.error(session) # expect {'x': 1}
    return ""

with app.test_request_context() as trc:
  with app.test_client() as c:
    with c.session_transaction() as sess:
      sess['x'] = 1
    c.post()

This works as expected, with the output being something like this:

ERROR:root:<SecureCookieSession {'x': 1}>

Unfortunately I am encountering an unexpected result where the session data is not set in the endpoint function, i.e. the output is something like this:

ERROR:root:<SecureCookieSession {}>

This issue exhibits only when run from my unit testing framework. As it stands, I am unable to reproduce this problem with a degenerate case, though I have made a fairly substantial effort with a gist of some of this effort here. The salient points being that I have included itsdangerous and Google App Engine testbed, expecting maybe one of them to have been the cause.

On my own system I have gone further than the gist, and almost completely replicated my unit test framework trying to isolate this. Likewise, I have removed ever-increasing amounts of relevant code from my testing framework. To the point, I am unable to think of differences between the degenerate case and my stripped-down framework that could influence the outcome. I have traversed the c.post() call in pdb to try eek out the cause of this malignity, but have yet to glean any useful insight.

Which is all to say, I would be grateful for a little direction or suggestion as to where the issue may lie. What could possibly be influencing the Werkzeug context in such a way that the session_transaction is not being honoured?

Answer 1

In my case, I was restricting cookies to a specific domain automatically by loading a configuration file. By updating the configuration on-the-fly, I was able to get cookies to work while unit testing. Setting the SESSION_COOKIE_DOMAIN property to None, all domains (namely localhost) were able to set sessions.

app.config.update(                                                     
    SESSION_COOKIE_DOMAIN = None                                                
)

You may want to fiddle around with the configuration settings described under Configuration Handling in the docs.

Answer 2

I hate to resurrect an old question, but I believe that I figured out the solution to this issue. For testing, try setting your server name to localhost:

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

I was originally using Brian's hack, but this solved the problem for me.