diff --git a/SpringBoot-Introduction/Lectures/Contents.md b/SpringBoot-Introduction/Lectures/Contents.md
index 9e31feb..fab1277 100644
--- a/SpringBoot-Introduction/Lectures/Contents.md
+++ b/SpringBoot-Introduction/Lectures/Contents.md
@@ -15,4 +15,5 @@
 - [비즈니스 요구사항 정리](https://github.com/banjjoknim/TIL/blob/master/SpringBoot-Introduction/Lectures/Lecture08.md)
 - [회원 도메인과 리포지토리 만들기](https://github.com/banjjoknim/TIL/blob/master/SpringBoot-Introduction/Lectures/Lecture09.md)
 - [회원 리포지토리 테스트 케이스 작성](https://github.com/banjjoknim/TIL/blob/master/SpringBoot-Introduction/Lectures/Lecture10.md)
-- [회원 서비스 개발](https://github.com/banjjoknim/TIL/blob/master/SpringBoot-Introduction/Lectures/Lecture11.md)
\ No newline at end of file
+- [회원 서비스 개발](https://github.com/banjjoknim/TIL/blob/master/SpringBoot-Introduction/Lectures/Lecture11.md)
+- [회원 서비스 테스트](https://github.com/banjjoknim/TIL/blob/master/SpringBoot-Introduction/Lectures/Lecture12.md)
\ No newline at end of file
diff --git a/SpringBoot-Introduction/Lectures/Lecture12.md b/SpringBoot-Introduction/Lectures/Lecture12.md
new file mode 100644
index 0000000..3931efa
--- /dev/null
+++ b/SpringBoot-Introduction/Lectures/Lecture12.md
@@ -0,0 +1,23 @@
+# 회원 서비스 테스트
+
+---
+
+## 테스트 클래스 작성
+- `Ctrl + Shift + T`
+- 테스트 코드는 과감하게 한글을 사용해도 된다(영어권 사람들과 일하는 것이 아니라면).
+- 빌드될 때 테스트 코드는 실제 코드에 포함되지 않는다.
+- `given`, `when`, `then` 주석을 권장하는 편이다.
+    - `given` : 무언가 상황이 주어졌을 때
+    - `when` : 이것을 실행하면
+    - `then` : 이러한 결과가 나와야 한다.
+- 테스트는 예외상황이 정상상황보다 더 중요하다.
+- `Ctrl + R` : 이전에 실행했던 것을 그대로 실행해준다(Mac).
+    - 윈도우는 `Shift + F10`을 사용한다.
+
+---
+
+## Dependency Injection(의존성 주입)
+- 직접 인스턴스를 만드는 것이 아니라 외부에서 넣어주는 것을 말한다.
+    - `MemberSerivce` 입장에서는 직접 `new`로 인스턴스를 만드는 것이 아니라 외부에서 `MemberRepository`를 넣어주는 것이다.
+    
+---
\ No newline at end of file
diff --git a/SpringBoot-Introduction/src/main/java/hello/springintroduction/service/MemberService.java b/SpringBoot-Introduction/src/main/java/hello/springintroduction/service/MemberService.java
index 31428a4..96d1d10 100644
--- a/SpringBoot-Introduction/src/main/java/hello/springintroduction/service/MemberService.java
+++ b/SpringBoot-Introduction/src/main/java/hello/springintroduction/service/MemberService.java
@@ -2,14 +2,17 @@ package hello.springintroduction.service;
 
 import hello.springintroduction.domain.Member;
 import hello.springintroduction.repository.MemberRepository;
-import hello.springintroduction.repository.MemoryMemberRepository;
 
 import java.util.List;
 import java.util.Optional;
 
 public class MemberService {
 
-    private final MemberRepository memberRepository = new MemoryMemberRepository();
+    private final MemberRepository memberRepository;
+
+    public MemberService(MemberRepository memberRepository) {
+        this.memberRepository = memberRepository;
+    }
 
     /*
      * 회원 가입
diff --git a/SpringBoot-Introduction/src/test/java/hello/springintroduction/service/MemberServiceTest.java b/SpringBoot-Introduction/src/test/java/hello/springintroduction/service/MemberServiceTest.java
new file mode 100644
index 0000000..8ec8530
--- /dev/null
+++ b/SpringBoot-Introduction/src/test/java/hello/springintroduction/service/MemberServiceTest.java
@@ -0,0 +1,68 @@
+package hello.springintroduction.service;
+
+import hello.springintroduction.domain.Member;
+import hello.springintroduction.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.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+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);
+        assertThatThrownBy(() -> memberService.join(member2))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("이미 존재하는 회원입니다.");
+
+        // then
+
+    }
+
+    @Test
+    void findMembers() {
+    }
+
+    @Test
+    void findOne() {
+    }
+}
\ No newline at end of file