🚀 3단계 - 테스트를 통한 코드 보호

src/test/java/kitchenpos/application/MenuGroupServiceTest.java

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+package kitchenpos.application;
+
+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.BDDMockito.given;
+
+import java.util.List;
+import kitchenpos.domain.MenuGroup;
+import kitchenpos.domain.MenuGroupRepository;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.NullAndEmptySource;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+@ExtendWith(MockitoExtension.class)
+class MenuGroupServiceTest {
+
+    @InjectMocks
+    private MenuGroupService menuGroupService;
+
+    @Mock
+    private MenuGroupRepository menuGroupRepository;
+
+    @DisplayName("메뉴 그룹 목록 조회")
+    @Nested
+    class FindAllMenuGroups {
+
+        @DisplayName("메뉴 그룹 목록 조회 성공하면 메뉴 그룹 목록을 반환한다.")
+        @Test
+        void if_success_then_return_menu_groups() {
+            // given
+            given(menuGroupRepository.findAll())
+                    .willReturn(List.of(new MenuGroup(), new MenuGroup()));
+
+            // when
+            var menuGroups = menuGroupService.findAll();
+
+            // then
+            assertThat(menuGroups).hasSize(2);
+        }
+    }
+
+    @DisplayName("메뉴 그룹 생성")
+    @Nested
+    class MenuGroupCreate {
+
+        @DisplayName("메뉴 그룹 이름이 null이거나 빈 문자열인 경우 예외를 던진다.")
+        @ParameterizedTest
+        @NullAndEmptySource
+        void if_name_is_null_or_empty_then_throw_exception(String name) {
+            // given
+            var request = new MenuGroup();
+            request.setName(name);
+
+            // when
+            assertThatThrownBy(() -> menuGroupService.create(request))
+                    // then
+                    .isInstanceOf(IllegalArgumentException.class);
+        }
+
+        @DisplayName("메뉴 그룹 생성 성공하면 메뉴 그룹을 반환한다.")
+        @ParameterizedTest
+        @ValueSource(strings = {"치킨", "사이드 메뉴", "음료"})
+        void if_success_then_return_menu_group(String name) {
+            // given
+            var request = new MenuGroup();
+            request.setName(name);
+            given(menuGroupRepository.save(any(MenuGroup.class)))
+                    .will(invocation -> invocation.getArgument(0));
+
+            // when
+            var menuGroup = menuGroupService.create(request);
+
+            // then
+            assertThat(menuGroup).isNotNull();
+            assertThat(menuGroup.getName()).isEqualTo(name);
+        }
+    }
+}