Worked on the fastapi/typer repository to enhance CLI testing by enabling explicit unsetting of environment variables within CliRunner.invoke. Addressed the challenge of test isolation by allowing None values to unset environment variables, which improved the reliability and clarity of CLI test semantics. Utilized Python and PyTest to implement this feature, focusing on robust environment variable handling and ensuring that tests run with greater consistency and fewer flaky outcomes. Demonstrated skills in CLI development and testing, collaborating through pull requests to maintain code quality. The work resulted in more flexible and dependable CLI test environments for ongoing development and maintenance.