기존에는 회원 서비스가 메모리 회원 리포지토리를 직접 생성하게 했다.

public class MemberService {

		private final MemberRepository memberRepository = new MemoryMemberRepository();
		
}

회원 서비스 코드를 DI 가능하게 변경한다.

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.AfterEach;
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
    void 회원가입() {
        // given
        Member member = new Member();
        member.setName("hello");

        // when
        Long saveId = memberService.join(member);

        // then
        Member findMember = memberService.findOne(saveId).get();
        assertThat(member.getName()).isEqualTo(findMember.getName());
    }

    @Test
    public void 중복_회원_예외() {
        // 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.

        // then
        assertThat(e.getMessage()).isEqualTo("이미 존재하는 회원입니다.");
    }
}