Add unit tests for parsers

**Problem**
When working with core, 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 parser implementation and any existing unit-test entry points in the repository. Clarify which parser errors need descriptive messages, then add focused coverage and verify that the resulting test suite passes.

Written by the indexing model from the issue text.