Add unit tests for data

**Problem**
When working with components, 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 file, test, or entry point is named in the issue. Start by locating the component error-handling paths and existing unit-test conventions, then determine which data cases lack coverage. Done means the requested cases have tests and error messages are sufficiently descriptive for debugging, as agreed in the issue discussion.

Written by the indexing model from the issue text.