### Question:
OrderService { @Transactional public void add(OrderDO order) { OrderDO exists = orderMapper.selectById(1); System.out.println(exists); orderMapper.insert(order); exists = orderMapper.selectById(1); System.out.println(exists); }  @Transactional void add(OrderDO order); OrderDO findById(Integer id);  }### Answer:
@Test public void testAdd() { OrderDO order = new OrderDO(); order.setUserId(20); orderService.add(order); }