django.test.client._session should check for session middleware instead

[Trevor Caira]

The django test client class allows you to use self.client.session only if you have 'django.contrib.sessions' in your INSTALLED_APPS setting. That is, it assumes you are using sessions if and only if you have the sessions app installed.

This assumption breaks down when you are using the sessions middleware independently of the sessions app, for instance if you are using a cache backend for sessions.

I propose that django.test.client._session check for the sessions middleware class in MIDDLEWARE_CLASSES instead of the sessions app in INSTALLED_APPS to make it easier for people using the session middleware independently of the sessions app to use self.client.sesssion in tests.

[Malcolm Tredinnick]

This looks like a reasonable request.

[Ramiro Morales]

In [16386]:

Fixed #7836 -- Modified strategy used by the test client to check for session functionality so it is useful in environments where the DB-based session backend isn't being used. Thanks trevor for the report.

[Ramiro Morales]

In [17739]:

Reverted r16386 because it replaced a brittle method with another not less
arbitrary method when the test client checks for the presence of the bundled
session backends+session middleware combination.

We will revisit the issue soon, probably to make these checks even less strict.

Refs #7836, #16605

[Unai Zalakain]

I'm probably missing something, where's the need of checking if some kind of session middleware exists? If not present, wouldn't {} be returned anyways?

BTW, shouldn't it be better if the engine module import happen outside _session and instead of checking for if coockie if cookie is not None is checked?

[Vlastimil Zíma]

Replying to unaizalakain:

I'm probably missing something, where's the need of checking if some kind of session middleware exists? If not present, wouldn't {} be returned anyways?

In application, the attribute request.session is created by SessionMiddleware. If missing you will get AttributeError.
In tests, you get either empty dictionary or SessionStore.

The problem here is no error is indicated by client when you don't have sessions installed, but client.login does not do a valid login. This is problem which is not quite easy to find.

BTW, shouldn't it be better if the engine module import happen outside _session and instead of checking for if coockie if cookie is not None is checked?

It wouldn't. You can change settings for the test and you want the test to use yours.

[Unai Zalakain]

What if _sesion arises an exception if no subclass of the session middleware is found?

[Claude Paroz]

I think that the recent commit 21dd98a3 fixing #25699 is also fixing this issue.