improve test cases

This issue has no description.

The issue body is empty, so start by examining the existing test suite in the repository to understand the current coverage and structure. Look for test files in the project, likely in a 'test' directory, and review the API calls managed by the library. Determine what areas need improvement, such as edge cases or error handling, and write new test cases accordingly. Verify changes by running the existing test suite to ensure they pass.

Written by the indexing model from the issue text.