### Question:
CategoryServiceImpl implements CategoryService { @Override public Optional<ProductCategory> findById(Integer categoryId) { return repository.findById(categoryId); }  @Override Optional<ProductCategory> findById(Integer categoryId); @Override List<ProductCategory> findAll(); @Override List<ProductCategory> findByCategoryTypeIn(List<Integer> categoryTypeList); @Override ProductCategory save(ProductCategory productCategory); @Override void delete(Integer categoryId);  }### Answer:
@Test public void findById() { Optional<ProductCategory> productCategory = categoryService.findById(1); System.out.println(productCategory); }