Multi db tests behave differently on different dbs

[obiwanus]

I have two identical sqlite databases for testing

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'first',
    },
    'second': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'second',
    },
}

At the start of each test the default database is clean, but the second database contains the data from the previous test runs.
The transaction setting pytestmark = pytest.mark.django_db(transaction=True) doesn't seem to have any effect on the default database behaviour - it is always clean for every test regardless of whether transaction is True or False. The same is true for the second database except it's always dirty.

[blueyed]

Are you using --reuse-db and/or --no-migrations?
What Django and pytest-django versions are you using?

IIRC Django only runs management commands (including migrations etc) on the default DB only.
Not sure about tests though - although we should be using Django's behavior/methods there already.

[obiwanus]

I'm not using --reuse-db or --no-migrations, just running pytest tests.

pytest-django==3.0.0, Django==1.10.3

My second database has no migrations, so I assume Django only does syncdb for it. I don't see though how this would affect tests - migrations should only be applied once before running the whole suite anyway, not between test runs, right?

[obiwanus]

I'll try to create a minimal working example to reproduce the issue on Monday

[obiwanus]

OK I've created a repo with a minimal example that should demonstrate the issue

https://github.com/obiwanus/pytest-django-bug

Please let me know if you have any problems with it. Thanks

[blueyed]

I think a failing test (as a PR) would be better. But the above might be enough for others to look at already.

[vbarbaresi]

Django only deals with the default database per default, as an optimization. Link to the doc
You have to wrap the test into a class and define multi_db = True for it to handle the 2 databases.

I found this in pytest-django doc: https://github.com/pytest-dev/pytest-django/blob/master/docs/database.rst#tests-requiring-multiple-databases

To implement the option in pytest-django without having to create classes, I hacked here:

diff --git a/pytest_django/fixtures.py b/pytest_django/fixtures.py
index 692e061..e95122e 100644
--- a/pytest_django/fixtures.py
+++ b/pytest_django/fixtures.py
@@ -119,6 +119,7 @@ def _django_db_fixture_helper(transactional, request, django_db_blocker):
     else:
         from django.test import TestCase as django_case

+    django_case.multi_db = True
     test_case = django_case(methodName='__init__')
     test_case._pre_setup()
     request.addfinalizer(test_case._post_teardown)

We could enable this on demand with a pytest.mark.multi_db marker, what do you think?

[blueyed]

@vbarbaresi
See #431.

[bluetech]

I'll close this issue as a duplicate of general multi-db support.