Multi-db: databases not being blocked

[meshy]

Hi!

I've found that databases are not always blocked when they should be in a multi-db setup. (Related to #924)

Allowing access to a single database can grant access to them all.

I've boiled this down to a minimal failing example, but I haven't yet found the cause or solution.

# test_example.py
import pytest
from django.db.transaction import atomic


@pytest.mark.django_db(databases=["default"])
def test_wrong_db():
    with pytest.raises(RuntimeError, match="Database access not allowed"):
        with atomic(using="secondary"):
            pass

# example_settings.py
import os

env = os.environ

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql_psycopg2",
        "NAME": env.get("DB_NAME", default="example"),
        "USER": env.get("DB_USER", default=""),
        "PASSWORD": env.get("DB_PASSWORD", default=""),
        "HOST": env.get("DB_HOST", default=""),
        "PORT": env.get("DB_PORT", default=5432),
        "TEST": {"NAME": env.get("DB_TEST_NAME", default="example-test")},
    },
    "secondary": {
        "ENGINE": "django.db.backends.postgresql_psycopg2",
        "NAME": env.get("DB2_NAME", default="secondary"),
        "USER": env.get("DB2_USER", default=""),
        "PASSWORD": env.get("DB2_PASSWORD", default=""),
        "HOST": env.get("DB2_HOST", default=""),
        "PORT": env.get("DB2_PORT", default=5432),
        "TEST": {"NAME": env.get("DB2_TEST_NAME", default="example-secondary-test")},
    },
}

================================ test session starts =================================
platform linux -- Python 3.10.12, pytest-8.2.2, pluggy-1.5.0
django: version: 5.0.6, settings: example_settings (from ini)
rootdir: /home/charlie/code/pytest-django-multidb
configfile: pyproject.toml
plugins: django-4.8.0
collected 1 item                                                                     

test_example.py F                                                              [100%]

====================================== FAILURES ======================================
___________________________________ test_wrong_db ____________________________________

    @pytest.mark.django_db(databases=["default"])
    def test_wrong_db():
>       with pytest.raises(RuntimeError, match="Database access not allowed"):
E       Failed: DID NOT RAISE <class 'RuntimeError'>

test_example.py:7: Failed
============================== short test summary info ===============================
FAILED test_example.py::test_wrong_db - Failed: DID NOT RAISE <class 'RuntimeError'>
================================= 1 failed in 0.24s ==================================

Versions in use:

• django==5.0.6
• psycopg==3.2.1
• pytest-django==4.8.0
• pytest==8.2.2