id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
31065	"""django.db.utils.InterfaceError: connection already closed""  in unittests"	Harm Verhagen	nobody	"I found a weird bug in Django that causes database errors when running unittesets,  this happens when doing nothing special/funky (see small included testcase)

= Steps to reproduce =

1. Start a new project `myproj`, with a new app `foo`
2. Edit {{{foo/tests.py}}}
{{{

from django.test import TestCase
from django.contrib.auth.models import User


class A(TestCase):
    """"""
    We have a tearDownClass() in this class without a matching setUpClass

    Removing the tearDownClass, or adding a setUpClass fixes/hides the problem
    """"""

    @classmethod
    def tearDownClass(cls):
        pass

    def test_foo(self):
        pass


class B(TestCase):

    def test_foo(self):
        pass


class C(TestCase):

    def test_foo(self):
        pass

    def setUp(self):
        User.objects.create_user('user', 'myemail@test.com', ""123"")
}}}

3. edit your `settings.py` to connect to a postgresql server
 (The problem does _not_ reproduce with the default sqlite config)

4.  {{{./manage.py test foo.tests.A foo.tests.B foo.tests.C}}}

(NB the order in which the tests are executed is important, in another order the problem does not reproduce)

= result =
{{{
$ ./manage.py test foo.tests.A foo.tests.B foo.tests.C
Creating test database for alias 'default'...
System check identified no issues (0 silenced).
..E
======================================================================
ERROR: test_foo (foo.tests.C)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/venv/lib/python3.5/site-packages/django/db/backends/base/base.py"", line 235, in _cursor
    return self._prepare_cursor(self.create_cursor(name))
  File ""/venv/lib/python3.5/site-packages/django/db/backends/postgresql/base.py"", line 223, in create_cursor
    cursor = self.connection.cursor()
psycopg2.InterfaceError: connection already closed

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File ""myproj/foo/tests.py"", line 39, in setUp
    User.objects.create_user('user', 'myemail@test.com', ""123"")
  File ""/env/lib/python3.5/site-packages/django/contrib/auth/models.py"", line 151, in create_user
    return self._create_user(username, email, password, **extra_fields)
  File ""/venv/lib/python3.5/site-packages/django/contrib/auth/models.py"", line 145, in _create_user
    user.save(using=self._db)
  File ""/venv/lib/python3.5/site-packages/django/contrib/auth/base_user.py"", line 66, in save
    super().save(*args, **kwargs)
  File ""/venv/lib/python3.5/site-packages/django/db/models/base.py"", line 741, in save
    force_update=force_update, update_fields=update_fields)
  File ""/venv/lib/python3.5/site-packages/django/db/models/base.py"", line 779, in save_base
    force_update, using, update_fields,
  File ""/venv/lib/python3.5/site-packages/django/db/models/base.py"", line 870, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File ""/venv/lib/python3.5/site-packages/django/db/models/base.py"", line 908, in _do_insert
    using=using, raw=raw)
  File ""/venv/lib/python3.5/site-packages/django/db/models/manager.py"", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File ""/venv/lib/python3.5/site-packages/django/db/models/query.py"", line 1186, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File ""/venv/lib/python3.5/site-packages/django/db/models/sql/compiler.py"", line 1366, in execute_sql
    with self.connection.cursor() as cursor:
  File ""/venv/lib/python3.5/site-packages/django/db/backends/base/base.py"", line 256, in cursor
    return self._cursor()
  File ""/venv/lib/python3.5/site-packages/django/db/backends/base/base.py"", line 235, in _cursor
    return self._prepare_cursor(self.create_cursor(name))
  File ""/venv/lib/python3.5/site-packages/django/db/utils.py"", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File ""/venv/lib/python3.5/site-packages/django/db/backends/base/base.py"", line 235, in _cursor
    return self._prepare_cursor(self.create_cursor(name))
  File ""/venv/lib/python3.5/site-packages/django/db/backends/postgresql/base.py"", line 223, in create_cursor
    cursor = self.connection.cursor()
django.db.utils.InterfaceError: connection already closed

----------------------------------------------------------------------
}}}



= expected result =
All tests pass

= notes =
* The problem does not reproduce with sqlite
* The problem goes away if you add a `@setUpClass`  to class `A`
* The problem goes away if you remove the `@tearDownClass` of class `A`
* The problem goes away if you change the order in which you execute the testclasses
* The problem goes away if you don't create the `User` in class `C`


= version info =
Seen on Django 2.2.8 and 2.2.6 
psycopg2==2.7.3.1
postgresql 10.10



"	Bug	closed	Database layer (models, ORM)	dev	Normal	invalid			Unreviewed	0	0	0	0	0	0