The sentinel object provides a convenient way of providing unique +objects for your tests.
+Attributes are created on demand when you access them by name. Accessing +the same attribute will always return the same object. The objects +returned have a sensible repr so that test failure messages are readable.
+The DEFAULT object is a pre-created sentinel (actually +sentinel.DEFAULT). It can be used by side_effect +functions to indicate that the normal return value should be used.
+Sometimes when testing you need to test that a specific object is passed as an +argument to another method, or returned. It can be common to create named +sentinel objects to test this. sentinel provides a convenient way of +creating and testing the identity of objects like this.
+In this example we monkey patch method to return +sentinel.some_object:
+>>> real = ProductionClass()
+>>> real.method = Mock(name="method")
+>>> real.method.return_value = sentinel.some_object
+>>> result = real.method()
+>>> assert result is sentinel.some_object
+>>> sentinel.some_object
+sentinel.some_object
+