Add unit tests for config

**Problem**
When working with lib, 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 configuration handling code under lib and identifying how its current errors are produced. Add unit coverage for the configuration error paths and make the resulting messages more descriptive, but the issue does not define the expected wording or name specific files and tests.

Written by the indexing model from the issue text.