Fixed tests isolation in logging_tests.

The SetupConfigureLogging test case does not restore the logging config
after its execution. It leaves the logger django.request with an empty
handlers array.

This also removes the last use of LOGGING_CONFIG, introduced in
43503b093a.

tests/logging_tests/tests.py

@@ -21,25 +21,6 @@ from django.views.debug import ExceptionReporter
 from . import views
 from .logconfig import MyEmailBackend
 
-# logging config prior to using filter with mail_admins
-OLD_LOGGING = {
-    'version': 1,
-    'disable_existing_loggers': False,
-    'handlers': {
-        'mail_admins': {
-            'level': 'ERROR',
-            'class': 'django.utils.log.AdminEmailHandler'
-        }
-    },
-    'loggers': {
-        'django.request': {
-            'handlers': ['mail_admins'],
-            'level': 'ERROR',
-            'propagate': True,
-        },
-    }
-}
-
 
 class LoggingFiltersTest(SimpleTestCase):
     def test_require_debug_false_filter(self):
@@ -483,13 +464,16 @@ class SetupConfigureLogging(SimpleTestCase):
     """
     Calling django.setup() initializes the logging configuration.
     """
-    @override_settings(
-        LOGGING_CONFIG='logging_tests.tests.dictConfig',
-        LOGGING=OLD_LOGGING,
-    )
     def test_configure_initializes_logging(self):
         from django import setup
-        setup()
+        try:
+            with override_settings(
+                LOGGING_CONFIG='logging_tests.tests.dictConfig',
+            ):
+                setup()
+        finally:
+            # Restore logging from settings.
+            setup()
         self.assertTrue(dictConfig.called)