Add unit tests for config

**Problem**
When working with controllers, 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 and controller error paths, then inspect any existing unit-test conventions. Define coverage for configuration behavior and detailed controller errors; done means the tests pass and failures expose the relevant context.

Written by the indexing model from the issue text.