Add unit tests for helpers

**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.

Start by locating the parser helpers and any existing unit tests, then inspect how parser failures currently produce error messages. Done means the relevant helper behavior has unit-test coverage and parser errors provide the more descriptive details requested by the issue.

Written by the indexing model from the issue text.