Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
-+--
   Reporter:  jsdalton   |Owner:  nobody
 Status:  new|Milestone:  1.3
  Component:  Contrib apps   |  Version:  SVN
 Resolution: | Keywords:
   Triage Stage:  Ready for checkin  |Has patch:  1
Needs documentation:  0  |  Needs tests:  0
Patch needs improvement:  0  |
-+--
Changes (by russellm):

 * stage:  Accepted => Ready for checkin


Comment:

 @rakuco -- Looks like it is.

 @jsdalton -- Thanks for the analysis; the sounds reasonable to me, and
 your patch looks good from first inspection. Marking RFC to remind me to
 take a look at getting this to trunk.

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Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
+--
   Reporter:  jsdalton  |Owner:  nobody
 Status:  new   |Milestone:  1.3
  Component:  Contrib apps  |  Version:  SVN
 Resolution:| Keywords:
   Triage Stage:  Accepted  |Has patch:  1
Needs documentation:  0 |  Needs tests:  0
Patch needs improvement:  0 |
+--

Comment (by rakuco):

 Hi there.

 Isn't this a duplicate of ticket #14105?

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Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
---+
  Reporter:  jsdalton  | Owner:  nobody
Status:  new   | Milestone:  1.3   
 Component:  Contrib apps  |   Version:  SVN   
Resolution:|  Keywords:
 Stage:  Accepted  | Has_patch:  1 
Needs_docs:  0 |   Needs_tests:  0 
Needs_better_patch:  0 |  
---+
Comment (by jsdalton):

 I was just reminded of this issue again this a.m. when I ran my tests
 against a fresh copy of the Django trunk and this problem popped up for me
 again.

 Given that this issue is causing failure in the contrib tests with a
 fairly typical configuration, I'd like to at a minimum suggest that the
 ticket gets marked as a blocker, to ensure a fix makes it into 1.3?

 If the patch I submitted needs improvement I'm open to additional
 suggestions, etc.

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Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
---+
  Reporter:  jsdalton  | Owner:  nobody
Status:  new   | Milestone:  1.3   
 Component:  Contrib apps  |   Version:  SVN   
Resolution:|  Keywords:
 Stage:  Accepted  | Has_patch:  1 
Needs_docs:  0 |   Needs_tests:  0 
Needs_better_patch:  0 |  
---+
Comment (by jsdalton):

 Thanks Russ.

 To clarify, for at least a few of the test errors related to this issue,
 the page is viewed multiple times in the same test *method*, e.g.
 RemoteUserTest.test_no_remote_user() in contrib.auth.tests. (I said test
 "run" above, which was inaccurate.) So it doesn't really matter whether we
 get the teardown right or not...the test needs to ensure the view is not
 cached in order to be run correctly. The same is true in a few of the
 other test methods (though I have not gone through and systematically
 analyzed whether the methods that are throwing errors are all calling the
 same view multiple times in a test method). So I think in this case
 ensuring the view is not cached is really the only satisfactory way. The
 only alternative would be to determine the cache key used to save the
 response and go in and delete it, which seems burdensome.

 I do agree with your overall point. We had a similar discussion on a
 similar issue #15026. The fact is, the Django test suite does an excellent
 job of restoring most of the major systems (e.g. DB, mail outbox) to their
 pre-test state state for each test method run, but cache (memcached at
 least) does not. I agree that calling flush() is problematic, because
 there are many examples where that would be undesirable behavior. I don't
 have any great ideas as to how one could clean up the cache after each
 test but only flush those keys that were set during that test, but maybe
 there's an idea lurking somewhere there...

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Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
---+
  Reporter:  jsdalton  | Owner:  nobody
Status:  new   | Milestone:  1.3   
 Component:  Contrib apps  |   Version:  SVN   
Resolution:|  Keywords:
 Stage:  Accepted  | Has_patch:  1 
Needs_docs:  0 |   Needs_tests:  0 
Needs_better_patch:  0 |  
---+
Changes (by russellm):

  * stage:  Unreviewed => Accepted

Comment:

 To clarify -- this only appears to be a problem for the memcache backend;
 locmem doesn't seem to cause any issues.

 I'm not completely convinced that @never_cache is the right solution here.
 Unit tests shouldn't require any special preparation to enable them to be
 test isolated -- the testing environment should provide those guarantees.
 However, any test involving caching will cause data to be put into a cache
 that can be easily lost.

 Django's test framework clears the database at the end of every test for
 exactly this reason; there is an argument that the cache should be flushed
 in the same way. However, I can see two problemw with this:

  1) Accidentially flushing a cache that contains other useful data (e.g.,
 the production cache)
  2) The cost of cache flushing when there is no cache used during a test.

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Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
---+
  Reporter:  jsdalton  | Owner:  nobody
Status:  new   | Milestone:  1.3   
 Component:  Contrib apps  |   Version:  SVN   
Resolution:|  Keywords:
 Stage:  Unreviewed| Has_patch:  1 
Needs_docs:  0 |   Needs_tests:  0 
Needs_better_patch:  0 |  
---+
Comment (by jsdalton):

 Oops, please ignore the first patch
 `cleanup_session_records_after_invalid_key_test.diff` and use
 `dont_cache_test_views.diff`. I accidentally uploaded the wrong patch, and
 I'm not sure how to delete it from trac.

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Re: [Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
---+
  Reporter:  jsdalton  | Owner:  nobody
Status:  new   | Milestone:  1.3   
 Component:  Contrib apps  |   Version:  SVN   
Resolution:|  Keywords:
 Stage:  Unreviewed| Has_patch:  1 
Needs_docs:  0 |   Needs_tests:  0 
Needs_better_patch:  0 |  
---+
Changes (by jsdalton):

  * needs_better_patch:  => 0
  * has_patch:  0 => 1
  * needs_docs:  => 0
  * needs_tests:  => 0
  * milestone:  => 1.3

Comment:

 I have traced the cause of these errors to some of the views that are
 created by contrib.auth and contrib.messages, in the urls.py file of each.
 These views are created for the purposes of running tests against them.

 The problem is that some of the these views are hit multiple times in a
 test run. When a view is hit a second time, the cache is returned to the
 test client (it would appear). In any case, the `context` attribute, which
 is normally set by the test client in the 'response` is not set (i.e. it
 is `None`) when a cache page is retrieved.. As a result, the tests cause
 an error like the one in the description of the ticket.

 My proposed solution to the problem is to affix the `@never_cache`
 decorator to the views created by the contrib apps for testing. These
 views are only used in testing, and no aspect of the caching system is
 tested during those test runs. In fact, the desired behavior of the views,
 per the test code, *is* to get a fresh response, with context.

 A patch with this solution is attached. Applying this patch and then re-
 running the tests with the setup described in the ticket description will
 result in a clean test run (no errors or failures).

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[Django] #15142: Contrib tests throwing errors on bare project when cache middleware enabled and cache specified

[Django]

#15142: Contrib tests throwing errors on bare project when cache middleware 
enabled
and cache specified
--+-
 Reporter:  jsdalton  |   Owner:  nobody
   Status:  new   |   Milestone:
Component:  Contrib apps  | Version:  SVN   
 Keywords:|   Stage:  Unreviewed
Has_patch:  0 |  
--+-
 I ran into an issue recently where the contrib tests were throwing
 multiple errors during a test run when cache middleware was enabled and a
 cache was specified.

 This is exactly the behavior described in this Stack Overflow question:
 http://stackoverflow.com/questions/3219668/using-django-cache-middleware-
 causes-contrib-auth-unit-tests-to-fail

 Here is a description of the setup and the steps to reproduce the problem
 (taken from that question):

 My Middleware:

 {{{
 MIDDLEWARE_CLASSES = (
 'django.middleware.cache.UpdateCacheMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.cache.FetchFromCacheMiddleware',
 )
 }}}

 All my test failures look like the one below:

 {{{
 ==
 Error: test_last_login
 (django.contrib.auth.tests.remote_user.RemoteUserTest)
 --
 Traceback (most recent call last):
   File "C:\Python26\lib\site-
 packages\django\contrib\auth\tests\remote_user.py",
  line 87, in test_last_login
 self.assertNotEqual(default_login,
 response.context['user'].last_login)
 TypeError: 'NoneType' object is unsubscriptable
 }}}

 Steps to Reproduce:

  1. Start a new django project (django-admin.py startproject myproject)
 and configure settings.py
  2. Add CACHE_BACKEND to settings.py and add the two Cache Middlewares
 from Django
  3. Run python manage.py test

 I have an idea as to the cause and a proposed patch to resolve this, but I
 will add it with a separate comment to keep the description of the issue
 clean here.

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