Using Mockito in SpringBoot App

Question

I am familiar with SpringBoot and I have written a small app. It has a ProductRepository extending CrudRepository. My ProductService is this:

public interface ProductService {
  Iterable<Product> listAllProducts();
  Product getProductById(Integer id);
  Product saveProduct(Product product);
  void deleteProduct(Integer id);
}

The ProductServiceImpl class auto wires in ProductRepository and provides implementation using ProductRepository.

My app is running as expected, and this is how I am testing the repository.

@RunWith(SpringRunner.class)
@SpringBootTest(classes = {RepositoryConfiguration.class})
public class ProductRepositoryTest {
  private ProductRepository productRepository;
  @Autowired
  public void setProductRepository(ProductRepository productRepository) {
    this.productRepository = productRepository;
  }
  @Test
  public void testSaveProduct(){
    //setup product
    Product product = new Product();
    product.setDescription("Shirt");
    product.setPrice(new BigDecimal("18.95"));
    product.setProductId("1234");        
    assertNull(product.getId()); //null before save
    productRepository.save(product);
    assertNotNull(product.getId()); //not null after save
    //fetch from DB
    Product fetchedProduct = productRepository.findOne(product.getId());
    //should not be null
    assertNotNull(fetchedProduct);      
 }
}

I want to know how I can unit test ProductRepository without external dependency (which the test above have and so don't qualify as a unit test. I believe it's more of an integration test).

Also, how I can unit test my ProductService? I tried mocking ProductRepository and Product with Mockito, like this:

public class ProductServiceImplTest {
  private ProductServiceImpl productServiceImpl;
  private ProductRepository productRepository;
  private Product product;

  @Before
  public void setupMock() {
    MockitoAnnotations.initMocks(this);
    productServiceImpl=new ProductServiceImpl();
    productRepository = mock(ProductRepository.class);
    product = mock(Product.class);
  }

  @Test
  public void testRetrieveById() throws Exception {
   when(productRepository.findOne(5)).thenReturn(product);
    assertEquals(product, productServiceImpl.getProductById(5));
  }
}

But this is what I get:

java.lang.NullPointerException
at    
  ProductServiceImpl.getProductById(ProductServiceImpl.java:24)
at  ProductServiceImplTest.testRetrieveById(ProductServiceImplTest.java:36)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at  sun.reflect.NativeMethodAccessorImpl.invoke
(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke
(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at  org.junit.runners.model.FrameworkMethod$1.runReflectiveCall
   (FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run
(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Am I using the Mockito.mock() correctly? Also what will be the difference if I use Mockito.spy() instead? Any help will be highly appreciated.

Answer 1

If you want to write unit tests then remove all those unnecessary annotations that are used for intergration testing.

Also you need to initiate the mocks in the @Before method:

public class ProductServiceImplTest {
  @InjectMocks
  private ProductServiceImpl productServiceImpl;
  @Mock
  private ProductRepository productRepository;
  @Mock
  private Product product;

  @Before
  public void setupMock() {
    MockitoAnnotations.initMocks(this);
  }

I think in your case, using mock should be enough.

The only time that you should use a spy is to invoke it on the class that you are testing which in your case would be:

productServiceImpl=new ProductServiceImpl();
prodServiceSpy = spy(productServiceImpl);

and mock some of the methods which implementation you do not want to be invoked, or invoke with a custom implementation required by the test scenario.