[Django] #36083: tests.file_storage.tests can fail when run in isolation

[Django]

#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
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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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