host-specific request breaks unrelated test cases - django

Question

I have the following tests:
from django.test import TestCase
from django.core.urlresolvers import reverse
class TestA(TestCase):
def test_a(self):
reverse('view1')
class TestB(TestCase):
def test_b(self):
self.client.get('/view2/', HTTP_HOST='second.test.net')
class TestC(TestCase):
def test_c(self):
reverse('view1')
TestA and TestB run successfully, but TestC breaks with
..E
======================================================================
ERROR: test_c (dhtest.tests.test_view2.TestC)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/phihag/dhtest/dhtest/tests/test_view2.py", line 14, in test_c
reverse('view1')
File "/home/phihag/.local/share/virtualenvs/dhtest---IwXRQ3/lib/python3.6/site-packages/django/urls/base.py", line 91, in reverse
return force_text(iri_to_uri(resolver._reverse_with_prefix(view, prefix, *args, **kwargs)))
File "/home/phihag/.local/share/virtualenvs/dhtest---IwXRQ3/lib/python3.6/site-packages/django/urls/resolvers.py", line 497, in _reverse_with_prefix
raise NoReverseMatch(msg)
django.urls.exceptions.NoReverseMatch: Reverse for 'view1' not found. 'view1' is not a valid view function or pattern name.
----------------------------------------------------------------------
Ran 3 tests in 0.006s
FAILED (errors=1)
But when I comment out TestB, TestC works! How do I fix this problem?
I'm using django-hosts with the following configuration:
from django.conf import settings
from django_hosts import patterns, host
host_patterns = patterns(
'',
host(
r'second\.test\.net',
'dhtest.secondurls',
name='second'
),
host(
r'(\w+)',
'dhtest.urls',
name='default'
),
)
and fairly simple URL files:
# dhtest/urls.py
from django.conf.urls import url
from django.http import HttpResponse
urlpatterns = [
url(r'^view1/', lambda _: HttpResponse('This is view1'), name='view1'),
]
# dhtest/secondurls.py
from django.conf.urls import url
from django.http import HttpResponse
urlpatterns = [
url(r'^view2/', lambda _: HttpResponse('view2 on another host')),
]
For reference, here is the full project.

Answer 1

This is a bug in Django-hosts. In its response middleware, django-hosts clobbers the thread-wide urlconf to that of the request.
In production, that is not a problem, because Django resets the urlconf to the default for every request, or the request-specific one.
But during the tests, after TestB there are no more requests coming, and reverse (and a bunch of other URL-related functions) are using the urlconf for a different host.
To work around this, restore the urlconf after any requests to specific hosts, like this:
class TestB(TestCase):
def test_b(self):
self.client.get('/view2/', HTTP_HOST='second.test.net')
def tearDown(self):
from django.urls.base import set_urlconf
set_urlconf(None)