Add unit tests for services

**Problem**
When working with components, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Start by locating the service components and any existing unit-test directories in the repository. Identify which component error cases need coverage and confirm the expected descriptive messages with the issue author; done means the relevant service tests cover those cases and pass.

Written by the indexing model from the issue text.