From 0dc6420b3ebddd7bc2a0059b225d54ac19d4d901 Mon Sep 17 00:00:00 2001
From: Jannis Leidel <jannis@leidel.info>
Date: Fri, 6 May 2011 13:29:24 +0000
Subject: [PATCH] Added TestCase.settings context manager to easily override
 settings in test methods.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16165 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/test/testcases.py                      | 19 +++++++++++-
 docs/topics/testing.txt                       | 25 ++++++++++++++++
 tests/regressiontests/settings_tests/tests.py | 30 +++++++++++++++++--
 3 files changed, 70 insertions(+), 4 deletions(-)

diff --git a/django/test/testcases.py b/django/test/testcases.py
index 8ce3a7af0f..d85bc27218 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -2,11 +2,12 @@ from __future__ import with_statement
 
 import re
 import sys
+from contextlib import contextmanager
 from functools import wraps
 from urlparse import urlsplit, urlunsplit
 from xml.dom.minidom import parseString, Node
 
-from django.conf import settings
+from django.conf import settings, UserSettingsHolder
 from django.core import mail
 from django.core.management import call_command
 from django.core.signals import request_started
@@ -341,6 +342,22 @@ class TransactionTestCase(ut2.TestCase):
         """
         restore_warnings_state(self._warnings_state)
 
+    @contextmanager
+    def settings(self, **options):
+        """
+        A context manager that temporarily sets a setting and reverts
+        back to the original value when exiting the context.
+        """
+        old_wrapped = settings._wrapped
+        override = UserSettingsHolder(settings._wrapped)
+        try:
+            for key, new_value in options.items():
+                setattr(override, key, new_value)
+            settings._wrapped = override
+            yield
+        finally:
+            settings._wrapped = old_wrapped
+
     def assertRedirects(self, response, expected_url, status_code=302,
                         target_status_code=200, host=None, msg_prefix=''):
         """Asserts that a response redirected to a specific URL, and that the
diff --git a/docs/topics/testing.txt b/docs/topics/testing.txt
index fbc6a7afe8..91d37b1bf1 100644
--- a/docs/topics/testing.txt
+++ b/docs/topics/testing.txt
@@ -1351,6 +1351,31 @@ For example::
 This test case will flush *all* the test databases before running
 ``testIndexPageView``.
 
+Overriding settings
+~~~~~~~~~~~~~~~~~~~
+
+.. method:: TestCase.settings
+
+.. versionadded:: 1.4
+
+For testing purposes it's often useful to change a setting temporarily
+and revert to the original value after running the testing code. For
+this use case Django provides a standard `Python context manager`_
+:meth:`~django.test.TestCase.settings`, which can be used like this::
+
+    from django.test import TestCase
+
+    class LoginTestCase(TestCase):
+        def test_overriding_settings(self):
+            with self.settings(LOGIN_URL='/other/login/'):
+                response = self.client.get('/sekrit/')
+                self.assertRedirects(response, '/other/login/?next=/sekrit/')
+
+This example will override the :setting:`LOGIN_URL` setting for the code
+in the ``with`` block and reset its value to the previous state afterwards.
+
+.. _`Python context manager`: http://www.python.org/dev/peps/pep-0343/
+
 Emptying the test outbox
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/regressiontests/settings_tests/tests.py b/tests/regressiontests/settings_tests/tests.py
index 12e1e2d9f6..175a17d2ff 100644
--- a/tests/regressiontests/settings_tests/tests.py
+++ b/tests/regressiontests/settings_tests/tests.py
@@ -1,8 +1,31 @@
 from django.conf import settings
-from django.utils import unittest
+from django.test import TestCase
 
+class SettingsTests(TestCase):
 
-class SettingsTests(unittest.TestCase):
+    def test_override(self):
+        settings.TEST = 'test'
+        self.assertEqual('test', settings.TEST)
+        with self.settings(TEST='override'):
+            self.assertEqual('override', settings.TEST)
+        self.assertEqual('test', settings.TEST)
+        del settings.TEST
+
+    def test_override_change(self):
+        settings.TEST = 'test'
+        self.assertEqual('test', settings.TEST)
+        with self.settings(TEST='override'):
+            self.assertEqual('override', settings.TEST)
+            settings.TEST = 'test2'
+        self.assertEqual('test', settings.TEST)
+        del settings.TEST
+
+    def test_override_doesnt_leak(self):
+        self.assertRaises(AttributeError, getattr, settings, 'TEST')
+        with self.settings(TEST='override'):
+            self.assertEqual('override', settings.TEST)
+            settings.TEST = 'test'
+        self.assertRaises(AttributeError, getattr, settings, 'TEST')
 
     #
     # Regression tests for #10130: deleting settings.
@@ -18,7 +41,8 @@ class SettingsTests(unittest.TestCase):
         self.assertRaises(TypeError, delattr, settings, '_wrapped')
 
 
-class TrailingSlashURLTests(unittest.TestCase):
+
+class TrailingSlashURLTests(TestCase):
     settings_module = settings
 
     def setUp(self):