Add unit tests for types

**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 code involved in type handling and the repository's existing unit-test setup. Identify the current error paths and expected messages, then add focused tests and improve the messages so failures are more descriptive; done means the tests pass and cover the relevant errors.

Written by the indexing model from the issue text.