存根存储库时获取 NullPointerException

Question

Hi I am trying to write some test for my app but I got stuck. I am getting NPE when stubbing my repository and I cant figure out why. The test is pointless but I want to understand what is wrong with it. Any help appriciated:)

Repo:

@Repository
public interface ItemRepository extends CrudRepository<Item, String> {}

Service:

@Service
public class ItemService {

    @Autowired
    ItemRepository itemRepository;

    @Autowired
    SteamMarketItemService steamMarketItemService;

    public void addItem(Item item) {
        itemRepository.save(item);
    }

    public List<Item> getAllItems() {
        return (List<Item>) itemRepository.findAll();
    }

Test:

@RunWith(MockitoJUnitRunner.class)
class ItemServiceTest {

    @Mock
    ItemRepository itemRepository;

    @InjectMocks
    ItemService itemService;

    @Test
    void getAllItems_shouldReturnListOfItems() {
        //given
        List<Item> itemList = Collections.singletonList(new Item());
        //when
        when(itemRepository.findAll()).thenReturn(itemList);
        List<Item> returnedItems = itemService.getAllItems();

        //then
        Assert.assertEquals(itemList,returnedItems);
    }
}

Error:

java.lang.NullPointerException
    at itemServiceTest.getAllItems_shouldReturnListOfItems(ItemServiceTest.java:34)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

Answer 1

You may need to use MockitoExtension

@Mocks are dependencies to your @InjectMocks reference. In this case, your annotation on Service and Repository are correct.

Here is how I am able to solve this if using JUnit5

package com.example.demo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import static org.mockito.ArgumentMatchers.any;

@ExtendWith(MockitoExtension.class)
class ItemServiceTests {

    @InjectMocks
    ItemService itemService;

    @Mock
    ItemRepository itemRepository;


    @Test
    void testItemServiceSaveItem() {
        Item item = new Item(312, "Test Mock");
        Mockito.when(itemRepository.save(item)).thenReturn(item);
        final Item saveItem = itemService.addItem(item);
        Mockito.verify(itemRepository, Mockito.times(1)).save(any(Item.class));
        Assertions.assertNotNull(saveItem, "Saved object cannot be null");
        Assertions.assertEquals(312, item.getId());
    }

    @Test
    void testGetItemListSuccess() {
        //given
        List<Item> itemList = Collections.singletonList(new Item());
        //when
        Mockito.when(itemRepository.findAll()).thenReturn(itemList);
        List<Item> returnedItems = itemService.getAllItems();
        //then
        Assertions.assertEquals(itemList, returnedItems);
    }

    @Test
    void testGetItemListFailure() {
        //given
        List<Item> itemList = Collections.singletonList(new Item());
        //when
        Mockito.when(itemRepository.findAll()).thenReturn(Arrays.asList(
                new Item(),
                new Item()
        ));
        List<Item> returnedItems = itemService.getAllItems();
        //then
        Assertions.assertNotEquals(itemList, returnedItems);
    }
    
}