Add TDD for success and custom ResourceNotFound exception

Author: codesungrape

src/test/java/com/codesungrape/hmcts/bookapi/BookServiceTest.java

@@ -2,6 +2,7 @@
 
 import com.codesungrape.hmcts.bookapi.dto.BookRequest;
 import com.codesungrape.hmcts.bookapi.entity.Book;
+import com.codesungrape.hmcts.bookapi.exception.ResourceNotFoundException;
 import com.codesungrape.hmcts.bookapi.repository.BookRepository;
 import com.codesungrape.hmcts.bookapi.service.BookService;
 import org.junit.jupiter.api.BeforeEach;
@@ -14,12 +15,14 @@
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
+import java.util.Optional;
 import java.util.UUID;
 import java.util.stream.Stream;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.when;
@@ -53,6 +56,10 @@ class BookServiceTest {
     private Book persistedBook;
     private UUID testId;
 
+    // --------------------------------------
+    // Parameter Sources
+    // --------------------------------------
+
     // Provide test data, static method: can be called without creating an object.
     private static Stream<Arguments> provideLongFieldTestCases() {
         UUID testId = UUID.randomUUID();
@@ -84,8 +91,9 @@ private static Stream<Arguments> provideLongFieldTestCases() {
         );
     }
 
-    // --------- TESTS ------------
-
+    // --------------------------------------
+    // Tests
+    // --------------------------------------
     @BeforeEach
     void setUp() {
         testId = UUID.randomUUID();
@@ -109,6 +117,9 @@ void setUp() {
                 .build();
     }
 
+    // --------------------------------------
+    // Tests: createBook
+    // --------------------------------------
     @Test
     void testCreateBook_Success() {
 
@@ -192,7 +203,6 @@ void testCreateBook_BlankTitle_ThrowsException() {
         );
     }
 
-    // --------- Repository failures
     @Test
     void testCreateBook_RepositoryFailure_ThrowsException() {
         // Arrange
@@ -213,7 +223,10 @@ void testCreateBook_RepositoryFailure_ThrowsException() {
     @ParameterizedTest(name = "{0}") // Display the test name
     @MethodSource("provideLongFieldTestCases")
     void testCreateBook_VeryLongFields_Success(
-        String testName, BookRequest request, Book expectedBook) {
+        String testName,
+        BookRequest request,
+        Book expectedBook
+    ) {
 
         // Arrange
         when(testBookRepository.save(any(Book.class))).thenReturn(expectedBook);
@@ -260,4 +273,50 @@ void testCreateBook_SpecialCharactersInTitle_Success() {
         // Did the service perform the correct action on its dependency?
         verify(testBookRepository, times(1)).save(any(Book.class));
     }
+
+    // --------------------------------------------------------------------------------------------
+    // Tests: deleteBookById(UUID)
+    // -------------------------------------------------------------------------------------------
+
+    @Test
+    void testDelete_Book_ShouldThrowException_WhenIdNotFound() {
+
+        // Arrange: As goal is to test what happens when the resource doesn't exist,
+        // we intentionally simulate DB returning NO result
+        when(testBookRepository.findByIdAndDeletedFalse(testId)).thenReturn(Optional.empty());
+
+        // ACT and ASSERT: throw ResourceNotFoundException when calling the delete method.
+        assertThrows(
+            // custom exception to reflect business rules vs technical problem
+            ResourceNotFoundException.class,
+            () -> testBookService.deleteBookById(testId)
+        );
+
+        // Assert: ensure the save method was NEVER called.
+        // proves delete business logic halts immediately when the resource isn't found.
+        verify(testBookRepository, never()).save(any(Book.class));
+    }
+
+    @Test
+    void testDeleteBookById_Success() {
+
+        // Arrange:
+        persistedBook.setDeleted(false); // ensure starting state
+
+        when(testBookRepository.findByIdAndDeletedFalse(testId))
+            .thenReturn(Optional.of(persistedBook));
+
+        when(testBookRepository.save(any(Book.class)))
+            .thenReturn(persistedBook);
+
+        // Act: call the service method we are testing
+        testBookService.deleteBookById(testId);
+
+        // Assert: the entity was marked deleted
+        assertTrue(persistedBook.isDeleted());
+
+        // Assert: repository methods were called correctly
+        verify(testBookRepository, times(1)).findByIdAndDeletedFalse(testId);
+        verify(testBookRepository, times(1)).save(persistedBook);
+    }
 }