Junit Mocking throwing Null pointer - junit

Question

I'm trying to mock the below service class.
I have created a separate Config bean which I'm calling as you can see below in the code:-
#Component
public class CrawlerService implements CrawlerServiceInterface {
private static final Logger LOGGER = LoggerFactory.getLogger(CrawlerService.class);
private final CrawlConfig config;
#Autowired
CrawlerFactory crawlerFactory;
#Autowired
public CrawlerService(#Qualifier(value = "CrawlerConfig") CrawlConfig config) {
this.config = config;
}
#Value("${com.prudential.noOfCrawlers}")
private int numberOfCrawlers;
#Override
public Object crawlService(String URL, int max) throws Exception {
LOGGER.info("In Service Class");
this.config.setMaxPagesToFetch(max);
PageFetcher pageFetcher = new PageFetcher(config);
RobotstxtConfig robotstxtConfig = new RobotstxtConfig();
RobotstxtServer robotstxtServer = new RobotstxtServer(robotstxtConfig, pageFetcher);
CrawlController controller = new CrawlController(config, pageFetcher, robotstxtServer);
controller.addSeed(URL);
controller.start(crawlerFactory, numberOfCrawlers);
List<Object> crawlersLocalData = controller.getCrawlersLocalData();
LOGGER.info("End of Service Class");
return crawlersLocalData;
}
}
The problem is that I'm getting a null pointer exception in this.config.setMaxPagesToFetch.
What am I doing wrong?
If I mocked some dependent object with #Mock annotation, does it mean it won't allow the value to be changed?
Here is the test class:-
List<Object> obj=new ArrayList<Object>();
#Mock
private CrawlConfig config;
#Mock
CrawlerFactory crawlerFactory;
#Mock
CrawlController controller;
#InjectMocks
CrawlerService crawlerService = new CrawlerService(config);
#Before
public void setUp() throws Exception {
MockitoAnnotations.initMocks(this);
}
#Test
public void testService() throws Exception {
when(controller.getCrawlersLocalData()).thenReturn(obj);
assertEquals(crawlerService.crawlService("https://vogella.com", 10), obj);
}

Answer 1

Here you have the problem with mock creating order. First of all, let's see what is happening here:
First, you are declaring some fields. In this case, you are declaring private CrawlConfig config and CrawlerService crawlerService. But crawlerService you don't just declare but initialize as well.
When you initialize it, you are passing as a dependency to it CrawlConfig config which is null.
Then MockitoAnnotations.initMocks(this) start doing it's magic. What does it do? It initializes all the fields annotated with #Mock, then it tries to initialize the #InjectMocks if it's not already initialized. In your case it is already initialized, so mockito won't initialize it and will use the instance which you created.
After that the mock injection takes part. Mockito will try to use any of it's strategy to inject mocks. You can read more about it in #InjectMocks javadoc. So in your case, mockito will try to use property setter or field injection. However, the CrawlConfig config in your CrawlerService is declared final, and mockito will ignore this field, as for this type of injection mockito ignores final or static fields.
So here you have created an instance of CrawlerService with dependency CrawlConfig config which is null and mockito won't do anything about it.
1) You can mock the CrawlConfig config by yourself before mockito is going to:
private CrawlConfig config = Mockito.mock(CrawlConfig.class);
#InjectMocks
CrawlerService crawlerService = new CrawlerService(config);
2) You can omit the initialization of the CrawlerService and rely on mockito:
#Mock
private CrawlConfig config = Mockito.mock(CrawlConfig.class);
#InjectMocks
CrawlerService crawlerService;
Each of these methods should work.
You can as well remove the final declaration from your CrawlerService and it will also work. But as for me, the two methods above are better options.