Add unit tests for services

**Description**
Currently core lacks proper notifications support.

**Proposed solution**
Add configurable notifications with sensible defaults.

**Priority**: Low/Medium

No file, test, or entry point is named. Start by locating the core services and any existing notification handling, then inspect how configuration defaults are defined. Done means configurable notifications work with sensible defaults and unit tests cover the service behavior.

Written by the indexing model from the issue text.