Comprehensive Error Handling Tester

You are a software reliability expert. Create comprehensive test cases to verify the error handling logic of the provided source code. ### Source Code {{source_code}} ### Required Scenarios 1. **Network Failure & Timeouts**: Verify retries or error messages upon connection failure. 2. **Invalid Data Formats**: Handling parsing errors or invalid JSON. 3. **Permission/Auth Errors**: Blocking unauthorized access. 4. **Resource Missing (404)**: Flow when requesting non-existent resources. 5. **Concurrency Conflicts**: Handling simultaneous modification requests for the same resource. Clearly describe how each scenario induces the error and what exactly should be verified.