Add unit tests for handlers

**Problem**
When working with utils, 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 or existing test paths are named. Start by locating the handlers and utils code, then find the current test layout and reproduce the error paths; done means unit tests cover the handlers and error messages provide the requested debugging detail.

Written by the indexing model from the issue text.