### Question:
CategoryServiceImpl implements CategoryService { public Category selectCategoryById(int id) { return categoryMapper.selectCategoryById(id); }  @Transactional(propagation=Propagation.REQUIRED,readOnly=true) List<Category> listAllCategory(); Category selectCategoryById(int id); void saveCategory(Category category); void updateCategory(Category category); Category findCategoryById(int id);  }### Answer:
@Test public void selectCategoryById(){ Category category = categoryService.selectCategoryById(2); System.out.println(category); }