Add unit tests for store

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

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

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

No file or test path is identified. Locate the store implementation and its existing tests, then trace the type-related error paths described in the issue; done means the relevant cases have unit coverage and produce the requested detailed messages.

Written by the indexing model from the issue text.