Add unit tests for controllers

**Problem**
When working with middleware, 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 controllers, middleware, and existing unit-test conventions in the repository. Trace the current middleware error paths, then add controller-focused tests and verify that the resulting errors are more descriptive and covered by the test suite.

Written by the indexing model from the issue text.