OrderServiceTest id to load is required for loading

[질문 템플릿]
1. 강의 내용과 관련된 질문인가요? (예)
2. 인프런의 질문 게시판과 자주 하는 질문에 없는 내용인가요? (예)
3. 질문 잘하기 메뉴얼을 읽어보셨나요? (예)

[질문 내용]
OrderServiceTest에서

id to load is required for loading

org.springframework.dao.InvalidDataAccessApiUsageException: id to load is required for loading

에러가 발생합니다. ID값이 왜 NULL인지 찾고 있는데 잘 모르겠네요.. 도움요청합니다.

 package jpabook.jpashop.service;

import jakarta.persistence.EntityManager;
import jpabook.jpashop.domain.Address;
import jpabook.jpashop.domain.Member;
import jpabook.jpashop.domain.Order;
import jpabook.jpashop.domain.OrderStatus;
import jpabook.jpashop.domain.item.Book;
import jpabook.jpashop.domain.item.Item;
import jpabook.jpashop.repository.OrderRepository;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.transaction.annotation.Transactional;

import static org.junit.jupiter.api.Assertions.*;

@SpringBootTest
@Transactional
class OrderServiceTest {

    @Autowired
    EntityManager em;
    @Autowired
    OrderService orderService;
    @Autowired
    OrderRepository orderRepository;

    @Test
    public void 상품주문() throws Exception {
        //given
        Member member = new Member();
        member.setName("회원1");
        member.setAddress(new Address("서울", "강가", "123-123"));
        em.persist(member);

        Book book = new Book();
        book.setName("시골 JPA");
        book.setPrice(10000);
        book.setStockQuantity(10);

        //when
        int orderCount = 2;
        Long orderId = orderService.order(member.getId(), book.getId(), orderCount);

        //then
        Order getOrder = orderRepository.findOne(orderId);

        assertEquals(OrderStatus.ORDER, getOrder.getStatus(), "상품 주문시 상태는 ORDER");
    }

    @Test
    public void 주문취소() throws Exception {
        //given

        //when

        //then
    }

    @Test
    public void 상품주문_재고수량초과() throws Exception {
        //given

        //when

        //then
    }
}

   Book book = new Book();
   book.setName("시골 JPA");
   book.setPrice(10000);
   book.setStockQuantity(10);

   // Persist the book to assign an ID
   em.persist(book);