Add unit tests for types

**Feature request**
It would be great to have notifications for middleware.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_notifications` with default `false`.

The title asks for unit tests for types, while the body requests middleware notifications and an enable_notifications config option defaulting to false. Start by locating the middleware and configuration entry points, then clarify which request is authoritative and identify the relevant test location before defining completion.

Written by the indexing model from the issue text.