Worked on refining feature implementation and test stability for the Xiangyu-Hu/SPHinXsys repository, focusing on improving the neighbor search mechanism. Refactored the NeighborBuilderContact component by encapsulating the radius check, replacing direct distance calculations with the kernel_->checkIfWithinCutOffRadius(displacement) method to enhance code clarity and maintainability. Updated regression test data to align with the new logic, ensuring continued test coverage and reliability. The work was implemented using C++ and leveraged software engineering best practices to improve encapsulation and robustness. These changes contributed to a more maintainable codebase and increased confidence in the accuracy of regression testing outcomes.