Add unit tests for store

**Problem**
When working with auth, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue names auth error handling and a store but gives no files, tests, or entry points. Start by locating the store and existing authentication error tests, then determine the expected descriptive messages. Done means the error behavior is clearer and unit tests cover the relevant store cases.

Written by the indexing model from the issue text.