Decorator for overriding settings while testing

Usage:
```
from tests.utils import set_settings

@set_settings(FOO='bar')
def test_something():
    ...
```

tests/utils.py

@@ -14,7 +14,9 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
+import functools
 
+from django.conf import settings
 from django.db.models import signals
 
 
@@ -34,3 +36,53 @@ def signals_switch():
 
 
 disconnect_signals, reconnect_signals = signals_switch()
+
+
+def set_settings(**new_settings):
+    """Decorator for set django settings that will be only available during the
+    wrapped-function execution.
+
+    For example:
+        @set_settings(FOO='bar')
+        def myfunc():
+            ...
+
+       @set_settings(FOO='bar')
+       class TestCase:
+           ...
+    """
+    def decorator(testcase):
+        if type(testcase) is type:
+            namespace = {"OVERRIDE_SETTINGS": new_settings, "ORIGINAL_SETTINGS": {}}
+            wrapper = type(testcase.__name__, (SettingsTestCase, testcase), namespace)
+        else:
+            @functools.wraps(testcase)
+            def wrapper(*args, **kwargs):
+                old_settings = override_settings(new_settings)
+                try:
+                    testcase(*args, **kwargs)
+                finally:
+                    override_settings(old_settings)
+
+        return wrapper
+
+    return decorator
+
+
+def override_settings(new_settings):
+    old_settings = {}
+    for name, new_value in new_settings.items():
+        old_settings[name] = getattr(settings, name, None)
+        setattr(settings, name, new_value)
+    return old_settings
+
+
+class SettingsTestCase(object):
+    @classmethod
+    def setup_class(cls):
+        cls.ORIGINAL_SETTINGS = override_settings(cls.OVERRIDE_SETTINGS)
+
+    @classmethod
+    def teardown_class(cls):
+        override_settings(cls.ORIGINAL_SETTINGS)
+        cls.OVERRIDE_SETTINGS.clear()