Fixed #27019 -- Made teardown_test_environment() restore the old DEBUG.

django/test/runner.py

@@ -9,7 +9,6 @@ import textwrap
 import unittest
 from importlib import import_module
 
-from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.db import DEFAULT_DB_ALIAS, connections
 from django.test import SimpleTestCase, TestCase
@@ -413,8 +412,7 @@ class DiscoverRunner(object):
         )
 
     def setup_test_environment(self, **kwargs):
-        setup_test_environment()
+        setup_test_environment(debug=self.debug_mode)
-        settings.DEBUG = self.debug_mode
         unittest.installHandler()
 
     def build_suite(self, test_labels=None, extra_tests=None, **kwargs):

django/test/utils.py

@@ -94,18 +94,28 @@ def instrumented_test_render(self, context):
     return self.nodelist.render(context)
 
 
-def setup_test_environment():
+class _SavedSettings(object):
+    pass
+
+
+def setup_test_environment(debug=None):
     """
     Perform global pre-test setup, such as installing the instrumented template
     renderer and setting the email backend to the locmem email backend.
     """
-    if hasattr(Template, '_original_render'):
+    if hasattr(_SavedSettings, 'debug'):
         # Executing this function twice would overwrite the saved values.
         raise RuntimeError(
             "setup_test_environment() was already called and can't be called "
             "again without first calling teardown_test_environment()."
         )
 
+    if debug is None:
+        debug = settings.DEBUG
+
+    _SavedSettings.debug = settings.DEBUG
+    settings.DEBUG = debug
+
     Template._original_render = Template._render
     Template._render = instrumented_test_render
 
@@ -129,6 +139,9 @@ def teardown_test_environment():
     Perform any global post-test teardown, such as restoring the original
     template renderer and restoring the email sending functions.
     """
+    settings.DEBUG = _SavedSettings.debug
+    del _SavedSettings.debug
+
     Template._render = Template._original_render
     del Template._original_render
 

docs/topics/testing/advanced.txt

@@ -612,11 +612,18 @@ Testing utilities
 To assist in the creation of your own test runner, Django provides a number of
 utility methods in the ``django.test.utils`` module.
 
-.. function:: setup_test_environment()
+.. function:: setup_test_environment(debug=None)
 
     Performs global pre-test setup, such as installing instrumentation for the
     template rendering system and setting up the dummy email outbox.
 
+    If ``debug`` isn't ``None``, the :setting:`DEBUG` setting is updated to its
+    value.
+
+    .. versionchanged:: 1.11
+
+        The ``debug`` argument was added.
+
 .. function:: teardown_test_environment()
 
     Performs global post-test teardown, such as removing instrumentation from