Denys Petrovskyi contributed to both front-end and back-end development, focusing on feature delivery and robust testing. On the koldovsky/1283-team-03 repository, he enhanced the blog highlights section by implementing a decorative wave divider and refining the layout using CSS and HTML, which improved user engagement and readability. In the GreenCityMVP21 repository, Denys developed comprehensive unit tests for controllers and mappers using Java, JUnit, and Mockito, targeting localization, CRUD operations, and data mapping. His work emphasized maintainability and reliability, reducing regression risk and supporting safer feature releases through detailed test coverage and thoughtful refactoring of test suites.