Add test cases for override_config

Test usage of override_config in different forms
Ensure flexibility between decorator and context manager

tests/test_test_utils.py

@@ -0,0 +1,34 @@
+from django.test import TestCase
+
+from constance import config
+from constance.test import override_config
+
+
+class OverrideConfigFunctionDecoratorTestCase(TestCase):
+    """Test that the override_config decorator works correctly.
+
+    Test usage of override_config on test method and as context manager.
+    """
+    def test_default_value_is_true(self):
+        """Assert that the default value of config.BOOL_VALUE is True."""
+        self.assertTrue(config.BOOL_VALUE)
+
+    @override_config(BOOL_VALUE=False)
+    def test_override_config_on_method_changes_config_value(self):
+        """Assert that the method decorator changes config.BOOL_VALUE."""
+        self.assertFalse(config.BOOL_VALUE)
+
+    def test_override_config_as_context_manager_changes_config_value(self):
+        """Assert that the context manager changes config.BOOL_VALUE."""
+        with override_config(BOOL_VALUE=False):
+            self.assertFalse(config.BOOL_VALUE)
+
+        self.assertTrue(config.BOOL_VALUE)
+
+
+@override_config(BOOL_VALUE=False)
+class OverrideConfigClassDecoratorTestCase(TestCase):
+    """Test that the override_config decorator works on classes."""
+    def test_override_config_on_class_changes_config_value(self):
+        """Asser that the class decorator changes config.BOOL_VALUE."""
+        self.assertFalse(config.BOOL_VALUE)