Developed Vitest fixtures support within the stryker-mutator/stryker-js repository, focusing on enhancing mutation testing workflows for projects using Vitest. The work involved updating the runner to enable proper object destructuring in lifecycle hooks such as beforeEach and afterAll, addressing fixture-related errors that previously caused unreliable test outcomes. Integration tests were implemented in TypeScript to validate the new fixture handling and ensure robust support for broader test patterns. By leveraging JavaScript, TypeScript, and Vitest, the changes improved reliability and reduced flaky failures in test suites, providing a more stable foundation for mutation testing in modern JavaScript and TypeScript projects.