Add unit tests for store

**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.

Locate the store middleware and any existing unit tests, then read how errors are currently created and reported. Clarify which middleware failures need more descriptive messages and add tests that define the expected wording; done means the selected cases are covered and the tests pass.

Written by the indexing model from the issue text.