Regression, faking TEST_MIRROR yields unusable REUSE_DB in django-nose 1.4

[wdoekes]

TLDR: If you "fake" a TEST_MIRROR config, by pointing it to the same database as the original, REUSE_DB is broken since django-nose 1.4.

See this settings.py:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'nosetest',
        'HOST': 'localhost',
        'USER': 'walter',
        'PASSWORD': os.environ.get('MYSQL_PASSWORD'),
    },
}
if os.environ.get('ISSUE'):
    DATABASES['web_db'] = DATABASES['default'].copy()

In django-nose 1.3, the following works fine:

$ REUSE_DB=1 ./manage.py test ./nosetest/test.py
nosetests ./nosetest/test.py --verbosity=1
Creating test database for alias 'default'...
Ran 2 tests in 0.019s
$ echo 'drop database test_nosetest;' | ./manage.py dbshell
(dropping the db again so we can see the issue)

So, that works with a single DB. Now try again, with the 2nd DB:

$ ISSUE=1 REUSE_DB=1 ./manage.py test ./nosetest/test.py
nosetests ./nosetest/test.py --verbosity=1
Creating test database for alias 'default'...
Ran 3 tests in 0.252s
$ echo 'drop database test_nosetest;' | ./manage.py dbshell
(dropping the db again so we can see the issue)

Awesome. That also works.

Now we update to django-nose 1.4:

$ REUSE_DB=1 ./manage.py test ./nosetest/test.py
nosetests ./nosetest/test.py --verbosity=1
Creating test database for alias 'default'...
Ran 2 tests in 0.064s
$ echo 'drop database test_nosetest;' | ./manage.py dbshell
(dropping the db again so we can see the issue)

Yes, without the 2nd DB, it works.

But now we try with the 2nd DB, and we get this:

$ ISSUE=1 REUSE_DB=1 ./manage.py test ./nosetest/test.py
nosetests ./nosetest/test.py --verbosity=1
Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
...
  File "/home/walter/.virtualenvs/nosetest/local/lib/python2.7/site-packages/MySQLdb/__init__.py", line 81, in Connect
    return Connection(*args, **kwargs)
  File "/home/walter/.virtualenvs/nosetest/local/lib/python2.7/site-packages/MySQLdb/connections.py", line 193, in __init__
    super(Connection, self).__init__(*args, **kwargs2)
_mysql_exceptions.OperationalError: (1049, "Unknown database 'test_nosetest'")

The cause is this change:

a893caf

If we remove those two lines, things start working again.

Now, you ask me: why do you point your TEST_MIRROR to the same DB? That's because we use a 2nd DB in production, but not on our dev machines.

---

Files used for this test:

==> req.txt <==
Django>=1.4,<1.5
django-nose==1.3
MySQL-python

==> nosetest/__init__.py <==

==> nosetest/models.py <==
from django.db import models

class MyModel(models.Model):
    value = models.IntegerField()

==> nosetest/settings.py <==
import os
INSTALLED_APPS = ['nosetest']
SECRET_KEY = 'A' * 50
TEST_RUNNER = 'django_nose.NoseTestSuiteRunner'
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'nosetest',
        'HOST': 'localhost',
        'USER': 'walter',
        'PASSWORD': os.environ.get('MYSQL_PASSWORD'),
    },
}
if os.environ.get('ISSUE'):
    DATABASES['web_db'] = DATABASES['default'].copy()

==> nosetest/test.py <==
import os
from django.db import connection
from django.test import TestCase
from .models import MyModel

class MyTestCase(TestCase):
    def setUp(self):
        MyModel.objects.create(value=42)

    def test_test(self):
        "Test model"
        self.assertEqual(MyModel.objects.all()[0].value, 42)

    if os.environ.get('ISSUE'):
        def test_2nd_db(self):
            "Test model on 2nd db"
            self.assertEqual(MyModel.objects.using('web_db')[0].value, 42)

    def test_transactions(self):
        "Has transaction/rollback support"
        self.assertTrue(connection.features.supports_transactions)

---

Note that if we point the 2nd DB to somewhere else, the REUSE_DB works. But then we run into the fact that TEST_MIRROR support is unavailable.