write exception handler in controller and test it successfully

backend/src/main/java/org/example/backend/ErrorMessage.java

@@ -0,0 +1,4 @@
+package org.example.backend;
+
+public record ErrorMessage(String message) {
+}

backend/src/main/java/org/example/backend/VocabController.java

@@ -1,12 +1,11 @@
 package org.example.backend;
 
 import lombok.RequiredArgsConstructor;
-import org.springframework.web.bind.annotation.GetMapping;
-import org.springframework.web.bind.annotation.PathVariable;
-import org.springframework.web.bind.annotation.RequestMapping;
-import org.springframework.web.bind.annotation.RestController;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.*;
 
 import java.util.List;
+import java.util.NoSuchElementException;
 
 @RestController
 @RequestMapping("/api/vocab")
@@ -24,4 +23,10 @@ public List<Vocab> getAllVocabs(){
     public Vocab getVocab(@PathVariable String _id){
         return vocabService.getVocab(_id);
     }
+
+    @ResponseStatus(HttpStatus.NOT_FOUND)
+    @ExceptionHandler(NoSuchElementException.class)
+    public ErrorMessage handleElementNotFoundException(){
+        return new ErrorMessage("No matches for given ID.");
+    }
 }

backend/src/test/java/org/example/backend/VocabControllerTest.java

@@ -52,4 +52,13 @@ void getVocab_shouldReturnSpecificVocab_whenCalledWithItsId() throws Exception {
                                           "info":"", "language":"Spanish", "reviewDates":[]}
                         """));
     }
+
+    @DirtiesContext
+    @Test
+    void getVocab_ShouldTriggerNotFoundStatus_whenCalledWithNonexistentID() throws Exception {
+        mvc.perform(MockMvcRequestBuilders.get("/api/vocab/000"))
+                .andExpect(status().isNotFound());
+    }
+
+
 }

backend/src/test/java/org/example/backend/VocabServiceTest.java

@@ -37,7 +37,7 @@ void getVocab_shouldReturnSpecificVocab_whenCalledWithItsId() {
     }
 
     @Test
-    void getVocab_shouldThrowNoSuchElementException_whenCalledWithNonexistantId() {
+    void getVocab_shouldThrowNoSuchElementException_whenCalledWithNonexistentId() {
         when(mockVocabRepo.findById("000")).thenThrow(NoSuchElementException.class);
         assertThrows(NoSuchElementException.class, () -> mockVocabRepo.findById("000"));
         verify(mockVocabRepo).findById("000");