기존에는 회원 서비스가 메모리 회원 리포지토리를 직접 생성하게 했다.

 public class MemberService {
     private final MemberRepository memberRepository =
                                           new MemoryMemberRepository();
}

public class MemberService {
     private final MemberRepository memberRepository;
     public MemberService(MemberRepository memberRepository) {
         this.memberRepository = memberRepository;
}
... }

회원 서비스 테스트


 package hello.hellospring.service;
 import hello.hellospring.domain.Member;
 import hello.hellospring.repository.MemoryMemberRepository;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import static org.assertj.core.api.Assertions.*;
 import static org.junit.jupiter.api.Assertions.*;
 class MemberServiceTest {
     MemberService memberService;
     MemoryMemberRepository memberRepository;
     @BeforeEach
     public void beforeEach() {
         memberRepository = new MemoryMemberRepository();
         memberService = new MemberService(memberRepository);
     }
     
      @AfterEach
    public void afterEach() {
        memberRepository.clearStore();
    }
@Test
public void 회원가입() throws Exception {
//Given
        Member member = new Member();
        member.setName("hello");
//When
        Long saveId = memberService.join(member);
//Then
        Member findMember = memberRepository.findById(saveId).get();
        assertEquals(member.getName(), findMember.getName());
    }
@Test
public void 중복_회원_예외() throws Exception {
//Given
        Member member1 = new Member();
        member1.setName("spring");
        Member member2 = new Member();
        member2.setName("spring");
//When
        memberService.join(member1);
        IllegalStateException e = assertThrows(IllegalStateException.class,
() -> memberService.join(member2));//예외가 발생해야 한다. assertThat(e.getMessage()).isEqualTo("이미 존재하는 회원입니다.");
}
}