Add unit tests for validation

**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.

Start by locating the utils validation code and its existing unit-test entry point. Review the current validation failures and error messages, then define tests for the relevant cases. Done means the validation behavior is covered and its errors provide more detailed debugging information.

Written by the indexing model from the issue text.