Add unit tests for services

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

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

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

No files, test paths, or entry points are named. Start by locating the parser services and their existing unit tests, then review how parser failures currently report errors; done means adding coverage for the services and producing more descriptive error messages.

Written by the indexing model from the issue text.