refactor: register method Optional 반환 -> Exception 처리

Optional 반환과 Exception 반환이 혼용되어 사용되고 있어, Exception 으로 통일

server/src/main/java/com/ticketing/server/user/application/UserController.java

@@ -33,14 +33,8 @@ public class UserController {
 
 	@PostMapping
 	public ResponseEntity<Object> register(@RequestBody @Valid SignUpRequest request) {
-		Optional<User> user = userService.register(request.toSignUp(passwordEncoder));
-
-		if (user.isEmpty()) {
-			log.error("이미 존재하는 이메일 입니다. :: {}", request.getEmail());
-			return ResponseEntity.status(HttpStatus.BAD_REQUEST).build();
-		}
-
-		return ResponseEntity.status(HttpStatus.CREATED).body(SignUpResponse.of(user.get()));
+		User user = userService.register(request.toSignUp(passwordEncoder));
+		return ResponseEntity.status(HttpStatus.CREATED).body(SignUpResponse.of(user));
 	}
 
 	@DeleteMapping

server/src/main/java/com/ticketing/server/user/service/UserServiceImpl.java

@@ -25,15 +25,14 @@ public class UserServiceImpl implements UserService {
 
 	@Override
 	@Transactional
-	public Optional<User> register(@Valid SignUpDTO signUpDto) {
+	public User register(@Valid SignUpDTO signUpDto) {
 		Optional<User> user = userRepository.findByEmail(signUpDto.getEmail());
 		if (user.isPresent()) {
 			log.error("이미 존재하는 이메일이기 때문에 신규 회원가입을 진행할 수 없습니다. :: {}", signUpDto);
-			return Optional.empty();
+			throw new IllegalArgumentException("이미 존재하는 이메일이기 때문에 신규 회원가입을 진행할 수 없습니다.");
 		}
 
-		User newUser = userRepository.save(signUpDto.toUser());
-		return Optional.of(newUser);
+		return userRepository.save(signUpDto.toUser());
 	}
 
 	@Override

server/src/main/java/com/ticketing/server/user/service/interfaces/UserService.java

@@ -9,7 +9,7 @@ import javax.validation.Valid;
 
 public interface UserService {
 
-	Optional<User> register(@Valid SignUpDTO signUpDto);
+	User register(@Valid SignUpDTO signUpDto);
 
 	Optional<User> delete(@Valid DeleteUserDTO deleteUser);
 

server/src/test/java/com/ticketing/server/user/service/UserServiceImplTest.java

@@ -1,6 +1,7 @@
 package com.ticketing.server.user.service;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.when;
 
@@ -49,10 +50,9 @@ class UserServiceImplTest {
 		when(userRepository.findByEmail("ticketing@gmail.com")).thenReturn(Optional.of(user));
 
 		// when
-		Optional<User> user = userService.register(signUp);
-
 		// then
-		assertThat(user).isEmpty();
+		assertThatThrownBy(() -> userService.register(signUp))
+			.isInstanceOf(IllegalArgumentException.class);
 	}
 
 	@Test
@@ -63,10 +63,10 @@ class UserServiceImplTest {
 		when(userRepository.save(any())).thenReturn(user);
 
 		// when
-		Optional<User> user = userService.register(signUp);
+		User user = userService.register(signUp);
 
 		// then
-		assertThat(user).isPresent();
+		assertThat(user).isNotNull();
 	}
 
 	@Test
@@ -98,20 +98,20 @@ class UserServiceImplTest {
 	@Test
 	@DisplayName("패스워드 변경 시 이메일이 존재하지 않을 경우")
 	void modifyPasswordFail() {
-	    // given
+		// given
 		when(userRepository.findByEmailAndIsDeletedFalse("ticketing@gmail.com")).thenReturn(Optional.empty());
 
-	    // when
+		// when
 		Optional<User> user = userService.modifyPassword(changePassword);
 
-	    // then
+		// then
 		assertThat(user).isEmpty();
 	}
 
 	@Test
 	@DisplayName("패스워드 변경 성공했을 경우")
 	void modifyPasswordSuccess() {
-	    // given
+		// given
 		when(userRepository.findByEmailAndIsDeletedFalse("ticketing@gmail.com")).thenReturn(Optional.of(user));
 
 		// when