#36083: tests.file_storage.tests can fail when run in isolation
-------------------------------------+-------------------------------------
     Reporter:  Adam Zapletal        |                     Type:  Bug
       Status:  new                  |                Component:  Testing
                                     |  framework
      Version:  dev                  |                 Severity:  Normal
     Keywords:                       |             Triage Stage:
                                     |  Unreviewed
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------
 The full test suite run with multiple threads passes for me, but when I
 run the `tests.file_storage.tests` file in isolation (`./runtests.py
 file_storage.tests`), I get a failure. It passes in isolation if I run the
 tests with only one thread (`./runtests.py --parallel 1
 file_storage.tests`). This happened to others when I asked about it in the
 Django Discord server, but not everyone. For what it's worth, I'm on the
 latest macOS running Python v3.12.

 When a failure happens, I get the following error:

 `django.core.exceptions.ImproperlyConfigured: AUTH_USER_MODEL refers to
 model 'auth.User' that has not been installed`

 I have narrowed the issue down to the fact that this test file contains a
 class that inherits from `LiveServerTestCase`. It seems like any test file
 that mixes `LiveServerTestCase` and something more normal like
 `unittest.TestCase` will fail for me when run in isolation with more than
 one thread.

 Here's a minimal example if anyone is interested:

 {{{#!python
 from unittest import TestCase

 from django.test import LiveServerTestCase


 class TestCaseTests(TestCase):
     def test(self):
         self.assertEqual(2, 2)


 class LiveServerTestCaseTests(LiveServerTestCase):
     available_apps = []

     def test(self):
         self.client.get(self.live_server_url + '/')
 }}}

 I have a fix, but I'm not sure if it's a good one. Setting `available_apps
 = ['django.contrib.auth']` on the `LiveServerTestCase`-based class fixes
 it as one would expect from the error message, but I wonder if this is
 hiding something like a race condition. I wonder why it passes the full
 test suite when run with multiple threads, but it can't pass in isolation
 when run with multiple threads.

 Should I open a pull request to fix
 
[https://github.com/django/django/blob/8bee7fa45cd7bfe70b68784314e994e2d193fd70/tests/file_storage/tests.py#L1241
 the test] in the way I mentioned above, or is something deeper going on
 here? It could be that I'm misunderstanding something about how
 `LiveServerTestCase` is isolated during test runs.
-- 
Ticket URL: <https://code.djangoproject.com/ticket/36083>
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