[feat] 과정에 강의 추가를 추가하라

과정에 강의가 새롭게 추가되므로 강의를 추가하는 로직을 만듭니다

src/main/java/nextstep/courses/domain/course/Course.java

@@ -1,5 +1,6 @@
 package nextstep.courses.domain.course;
 
+import nextstep.courses.domain.course.session.Session;
 import nextstep.courses.domain.course.session.Sessions;
 
 import java.time.LocalDateTime;
@@ -11,7 +12,7 @@ public class Course {
 
     private Long creatorId;
 
-    private Sessions sessions;
+    private Sessions sessions = new Sessions();
 
     private LocalDateTime createdAt;
 
@@ -30,6 +31,19 @@ public Course(Long id, String title, Long creatorId, LocalDateTime createdAt, Lo
         this.creatorId = creatorId;
         this.createdAt = createdAt;
         this.updatedAt = updatedAt;
+        this.sessions = new Sessions();
+    }
+
+    public int sessionSize() {
+        return this.sessions.size();
+    }
+
+    public void addSession(Session session) {
+        this.sessions.add(session);
+    }
+
+    public Long getId() {
+        return id;
     }
 
     public String getTitle() {

src/main/java/nextstep/courses/domain/course/session/Sessions.java

@@ -1,11 +1,16 @@
 package nextstep.courses.domain.course.session;
 
+import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
 
 public class Sessions implements Iterable<Session> {
     private final List<Session> sessions;
 
+    public Sessions() {
+        this(new ArrayList<>());
+    }
+
     public Sessions(List<Session> sessions) {
         validate(sessions);
 
@@ -22,8 +27,16 @@ private void checkSessionsSizeIsValid(List<Session> sessions) {
         }
     }
 
+    public int size() {
+        return this.sessions.size();
+    }
+
+    public void add(Session session) {
+        this.sessions.add(session);
+    }
+
     @Override
     public Iterator<Session> iterator() {
-        return null;
+        return this.sessions.iterator();
     }
 }

src/main/java/nextstep/courses/service/CourseService.java

@@ -0,0 +1,23 @@
+package nextstep.courses.service;
+
+import nextstep.courses.domain.course.Course;
+import nextstep.courses.domain.course.CourseRepository;
+import nextstep.courses.domain.course.session.Session;
+import org.springframework.stereotype.Service;
+
+import javax.annotation.Resource;
+
+@Service("courseService")
+public class CourseService {
+    @Resource(name = "courseRepository")
+    private CourseRepository courseRepository;
+
+    public void addSession(long courseId, Session session) {
+        Course course = getCourse(courseId);
+        course.addSession(session);
+    }
+
+    private Course getCourse(long courseId) {
+        return courseRepository.findById(courseId);
+    }
+}

src/test/java/nextstep/courses/domain/course/service/CourseServiceTest.java

@@ -0,0 +1,68 @@
+package nextstep.courses.domain.course.service;
+
+import nextstep.courses.domain.course.Course;
+import nextstep.courses.domain.course.CourseRepository;
+import nextstep.courses.domain.course.image.Image;
+import nextstep.courses.domain.course.session.Applicants;
+import nextstep.courses.domain.course.session.Duration;
+import nextstep.courses.domain.course.session.Session;
+import nextstep.courses.domain.course.session.SessionRepository;
+import nextstep.courses.service.CourseService;
+import nextstep.courses.service.SessionService;
+import nextstep.payments.domain.Payment;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+public class CourseServiceTest {
+    private Image image;
+    private Payment payment;
+    private LocalDate localDate;
+    private LocalDateTime localDateTime;
+    private Duration duration;
+    private Course course;
+    private Session session;
+
+    @BeforeEach
+    void setUp() {
+        course = new Course("math", 1L);
+        image = new Image(1000, "jpeg", Image.WIDTH_MIN, Image.HEIGHT_MIN);
+        payment = new Payment("1", 1L, 3L, 1000L);
+        localDate = LocalDate.of(2023, 12, 5);
+        localDateTime = LocalDateTime.of(2023, 12, 5, 12, 0);
+        duration = new Duration(localDate, localDate);
+        session = new Session(1L, image, duration, Session.Type.FREE, 1000L,
+                10, new Applicants(), Session.Status.RECRUIT, localDateTime, localDateTime);
+    }
+
+    @Mock
+    private SessionRepository sessionRepository;
+
+    @Mock
+    private CourseRepository courseRepository;
+
+    @InjectMocks
+    private CourseService courseService;
+
+    @Test
+    @DisplayName("주어진 강의를 과정에 추가하면 과정에 강의가 추가된다.")
+    void addSession_success() {
+        when(courseRepository.findById(course.getId())).thenReturn(course);
+        assertThat(course.sessionSize()).isEqualTo(0);
+
+        courseService.addSession(course.getId(), session);
+        assertThat(course.sessionSize()).isEqualTo(1);
+    }
+}