Refs #16281 -- Fixed isolation of admin_views.ViewOnSiteTests.

We were seeing this occasional failure in FlatpagesSitemapTests.setUpClass(),
which was unexpectedly attempting a write on the "other" database because
of an instance hint from a cached Site:

django.test.testcases.DatabaseOperationForbidden:
Database queries to 'other' are not allowed in this test. Add 'other' to flatpages_tests.test_sitemaps.FlatpagesSitemapTests.databases to
ensure proper test isolation and silence this failure.

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/admin_views/test_multidb.py b/tests/admin_views/test_multidb.py
index 0f18aeb315..870d434b02 100644
--- a/tests/admin_views/test_multidb.py
+++ b/tests/admin_views/test_multidb.py
@@ -3,6 +3,7 @@ from unittest import mock
 from django.contrib import admin
 from django.contrib.auth.models import User
 from django.contrib.contenttypes.models import ContentType
+from django.contrib.sites.models import Site
 from django.http import HttpResponse
 from django.test import TestCase, override_settings
 from django.urls import path, reverse
@@ -193,6 +194,11 @@ class ViewOnSiteRouter:
 class ViewOnSiteTests(TestCase):
     databases = {"default", "other"}
 
+    def tearDown(self):
+        # Reads via ViewOnSiteRouter may prime the global SITE_CACHE using the
+        # "other" db, which is problematic for other tests that do not use it.
+        Site.objects.clear_cache()
+
     def test_contenttype_in_separate_db(self):
         ContentType.objects.using("other").all().delete()
         book = Book.objects.using("other").create(name="other book")