Fixed #27032 -- Prevented setup_test_environment() from being called twice.

tests/test_utils/tests.py

@@ -20,6 +20,7 @@ from django.test import (
 from django.test.html import HTMLParseError, parse_html
 from django.test.utils import (
     CaptureQueriesContext, isolate_apps, override_settings,
+    setup_test_environment,
 )
 from django.urls import NoReverseMatch, reverse
 from django.utils import six
@@ -864,6 +865,13 @@ class SecondUrls:
     urlpatterns = [url(r'second/$', empty_response, name='second')]
 
 
+class SetupTestEnvironmentTests(SimpleTestCase):
+
+    def test_setup_test_environment_calling_more_than_once(self):
+        with self.assertRaisesMessage(RuntimeError, "setup_test_environment() was already called"):
+            setup_test_environment()
+
+
 class OverrideSettingsTests(SimpleTestCase):
 
     # #21518 -- If neither override_settings nor a setting_changed receiver