Add unit tests for data

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

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

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

No files or tests are named, and the title conflicts with the feature request. Start by locating the controller configuration entry point and existing unit-test patterns, then clarify the notification behavior with maintainers. Done should include the agreed controller notifications and tests showing enable_notifications defaults to false.

Written by the indexing model from the issue text.