Preprocessing functions for test client

[wbrackenbury]

Is there a reason that the Flask application preprocess_request() methods aren't currently called in the TestCase _pre_setup() method?

Use case: I want to test whether OAuth2 authorization is occurring correctly, and I want to be able to examine the state of the OAuth2 session in a test case. For the Google OAuth2Blueprint, however, this is loaded as follows (found in Flask-Dance, /contrib/google.py):

    google_bp = OAuth2ConsumerBlueprint("google", __name__,
        client_id=client_id,
        client_secret=client_secret,
        scope=scope,
        base_url="https://www.googleapis.com/",
        authorization_url="https://accounts.google.com/o/oauth2/auth",
        token_url="https://accounts.google.com/o/oauth2/token",
        auto_refresh_url=auto_refresh_url,
        redirect_url=redirect_url,
        redirect_to=redirect_to,
        login_url=login_url,
        authorized_url=authorized_url,
        authorization_url_params=authorization_url_params,
        session_class=session_class,
        backend=backend,
    )
    @google_bp.before_app_request
    def set_applocal_session():
        ctx = stack.top
        ctx.google_oauth = google_bp.session

...

google = LocalProxy(partial(_lookup_app_object, "google_oauth"))

This registers a function in the main Flask application that loads in the OAuth session upon each new request.

With a regular client, this yields no issues, as seen in the Flask application method (found in Flask, app.py)

    def full_dispatch_request(self):
        """Dispatches the request and on top of that performs request
        pre and postprocessing as well as HTTP exception catching and
        error handling.

        .. versionadded:: 0.7
        """
        self.try_trigger_before_first_request_functions()
        try:
            request_started.send(self)
            rv = self.preprocess_request()
            if rv is None:
                rv = self.dispatch_request()
        except Exception as e:
            rv = self.handle_user_exception(e)
        return self.finalize_request(rv)

As the self.preprocess_request() line loads the session into the context.

_pre_setup() currently reads, however:

    def _pre_setup(self):
        self.app = self.create_app()

        self._orig_response_class = self.app.response_class
        self.app.response_class = _make_test_response(self.app.response_class)

        self.client = self.app.test_client()

        self._ctx = self.app.test_request_context()
        self._ctx.push()

Which yields a RequestContext object, but does not wrap it with preprocessing.

Therefore, within a test case, if you try and print the imported session, you receive the error:

   File "/usr/local/lib/python3.5/site-packages/werkzeug/local.py", line 348, in __getattr__
     return getattr(self._get_current_object(), name)
   File "/usr/local/lib/python3.5/site-packages/werkzeug/local.py", line 307, in _get_current_object
     return self.__local()
   File "/usr/local/lib/python3.5/site-packages/flask/globals.py", line 45, in _lookup_app_object
     return getattr(top, name)
 AttributeError: 'AppContext' object has no attribute 'google_oauth'

However, if you save the application as an instance variable, and manually call the function preprocess_request(), it succeeds.

I'm new at this, so I'm not sure of the wider implications of this, or whether this is a correct solution. In general, though, would calling preprocess_request() in _pre_setup() potentially induce negative side effects?