Worked on the picnixz/cpython repository to address a critical issue in the unittest framework, focusing on exit code handling when setUpClass raises exceptions. Applied Python programming and test-driven development practices to update the main unittest runner logic, ensuring that failures during test setup now produce correct non-zero exit statuses. This change improved the reliability of both continuous integration pipelines and local validation by making error propagation more predictable for developers. Added targeted regression tests to prevent recurrence of the issue and enhanced maintainability by providing clear commit references and precise unit testing coverage throughout the codebase during the development period.