Add unit tests for utils

**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.

The issue names no files, tests, or entry points. Start by locating the parser utilities and their existing tests, then identify current error-handling paths; done means unit tests cover the relevant failures and the resulting messages are more descriptive.

Written by the indexing model from the issue text.