GridFsTemplate NullPointerException in Service Unit Test Class (Tech Stack: Spring Data / Spring Boot / Micro Service / Mongodb ) - spring

Question

I am developing a spring boot app.
The service method uploads a PDF into a mongodb repo using GridFsTemplate which is autowired in the service.
This file upload service method works as expected via postman rest client.
But, When I tried running a unit test; calling the same service method, the SpringData GridFsTemplate is not initialised (In MongoDB, you can use GridFS to store binary files). This results in the org.springframework.data.mongodb.gridfs.GridFsTemplate.store(...) throwing a NullPointerException.
Please, can you help, I have been stuck in this for a days.
Below is my service implementation:
#Service
public final class UploadServiceImpl implements UploadService {
#Autowired
private SequenceRepository sequenceDao;
#Autowired (required = true)
private GridFsTemplate gridFsTemplate;
#Override
public Long uploadFile(Invoice uploadedInvoice) {
ByteArrayInputStream byteArrayInputStream = null;
if (checkContentType(invoiceInfo.getContentType())) {
invoiceInfo.setPaymentID(sequenceDao.getNextSequenceId(INVOICE_UPLOAD_SEQ_KEY));
byteArrayInputStream = new ByteArrayInputStream(uploadedInvoice.getFileContent());
//Error thrown is java.lang.NullPointerException: null, where gridFsTemplate is null and basically autowire does not work when test is run.
GridFSFile gridFSUploadedFile= gridFsTemplate.store(byteArrayInputStream, invoiceInfo.getFileName(), invoiceInfo.getContentType(), invoiceInfo);
return 1l;
} else {
return 2l;
}
}
### Below is my Unit Test class for the service
#RunWith(MockitoJUnitRunner.class)
#ContextConfiguration
public class UploadServiceTest {
#Mock
private SequenceRepository sequenceRepositoryMock;
#Autowired
private GridFsTemplate gridFsTemplateMock;
#Mock
private Invoice invoiceMock;
#InjectMocks
private static UploadService uploadService = new UploadServiceImpl();
DBObject fileMetaData = null;
DB db = null;
Jongo jongo = null;
#Before
public void setUp() throws Exception {
db = new Fongo("Test").getDB("Database");
jongo = new Jongo(db);
}
#Test
public void testUploadFile() {
//test 1
Long mockPaymentNo = new Long(1);
Mockito.when(sequenceRepositoryMock.getNextSequenceId(INVOICE_SEQUENCE)).thenReturn(mockPaymentNo);
assertEquals(mockPaymentNo, (Long) sequenceRepositoryMock.getNextSequenceId(INVOICE_SEQUENCE));
//test 2
Invoice dummyInvoice = getDummyInvoice();
InvoiceInfo dummyInvoiceInfo = dummyInvoice.getInvoiceInfo();
MongoCollection invoicesCollection = jongo.getCollection("invoices");
assertNotNull(invoicesCollection.save(dummyInvoiceInfo));
assertEquals(1, invoicesCollection.save(dummyInvoiceInfo).getN());
System.out.println("TEST 2 >>>>>>>>>>>>>>>>>> "+ uploadService);
//test 3 : The following line is the cause of the exception, the service method is called but the GridFsTemplate is not initialized when the test is run. But it works when the endpoint is invoked via postman
uploadService.uploadFile(dummyInvoice);
System.out.println("TEST 3 >>>>>>>>>>>>>>>>>> ");
}
}

Answer 1

The problem is because you use #InjectMocks to autowire your UploadService.
And UploadService autowire two other beans SequenceRepository and GridFsTemplate.
If you’re doing TDD or not (and we are able to change the test first)
– clients of this code don’t know about an additional dependency,
because it’s completely hidden
The Javadoc states:
Mockito will try to inject mocks only either by constructor injection,
setter injection, or property injection in order and as described
below. If any of the following strategy fail, then Mockito won’t
report failure; i.e. you will have to provide dependencies yourself.
The solution is to use UploadServiceImpl constructor to autowire beans:
#Service
public final class UploadServiceImpl implements UploadService {
private final SequenceRepository sequenceDao;
private final GridFsTemplate gridFsTemplate;
private final PlannerClient plannerClient;
#Autowired
public PlannerServiceImpl(PlannerClient plannerClient, GridFsTemplate gridFsTemplate, SequenceRepository sequenceDao) {
this.plannerClient = plannerClient;
}
...
}
When there are more dependencies needed, they’re clearly in sight because they are initialized in constructor
More detailed:
https://tedvinke.wordpress.com/2014/02/13/mockito-why-you-should-not-use-injectmocks-annotation-to-autowire-fields/