Expose fixtures to change Django's {Transaction,}TestCase

[blueyed]

This adds django_db_testcase and django_transactional_db_testcase,
which allows to override them to e.g. enable the multi_db feature:

@pytest.fixture
def django_db_testcase(django_db_testcase):
    django_db_testcase.multi_db = True
    return django_db_testcase

Ref: #397

TODO:

• doc
• test(s) - not sure what should be tested here? Maybe the multi_db feature (which requires to setup multiple DBs though)

[blueyed]

Not really required for multi_db after all, in case you want to change it globally (#397 (comment)).

This PR makes still sense, and is needed in case you want to use some specialized/derived class, especially since it's only required for a subset of tests usually:

from django.test import TestCase

class MultiDbTestCase(TestCase):
    multi_db = True

@pytest.fixture
def django_db_testcase():
    return MultiDbTestCase

[Alphare]

Is there any way I could help with furthering the support for multiple databases?
I have a multi-tenant system with a connection for each tenant and I need to get testing quite soon.

[callmesangio]

+1
Having this merged would be great!
I'm finding myself dealing with django and multiple DBs...

[chris-erickson]

We'd like to support read replicas on Amazon Aurora/Postgres and this is one impediment to doing it confidently. We have a vast test suite that would be a lot of work to rework with the Django TestCase. I've tried various versions of ideas suggested here and none seem to solve the multi-db problem.

However, if I write a router with

    def db_for_read(self, model, **hints):
        return "default"

    def db_for_write(self, model, **hints):
        return "default"

it works as one would expect. Of course this doesn't really test multiple databases in the way one would want, but I think that's more of a system dynamics problem that I assume is accounted for (replica lag and it's ramifications).

Any clarity on the "best" way to hack this in right now would also be appreciated, I see a few different examples but none seem to do it, that I've tried.

[bluetech]

In my opinion this is a bit of a cop-out, I'd like us to try and provide proper interfaces as much as we can. The major one ATM it seems is multi-db support (database attribute), let's work on supporting that (there are many issues tracking that). So I'll close this for now.