Add unit tests for store

**Problem**
When working with validation, 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 store implementation and its validation and error-handling paths, then check for any existing unit-test patterns nearby. Done means adding tests that demonstrate descriptive validation errors and confirming the relevant test suite passes.

Written by the indexing model from the issue text.