Add unit tests for store

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

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

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

Start by locating the store implementation, handler code, configuration parsing, and existing unit tests; the payload does not name specific files. Determine how handler notifications should behave and where enable_notifications belongs, then cover the default false setting and the agreed notification behavior with tests.

Written by the indexing model from the issue text.