Spring Data MongoDB: Unit tests with Fongo

I am trying to test a mongo document persister using Junit along with Fongo. I am able to inject MongoTemplate to the class to be tested. But the call mongotemplate.getCollection("testCollection") returns null. I am not sure how to load the collection also for the unit testing.

Class to be tested :-

@Component
@Doc
public class MongoPersisterBean {

    @Autowired
    protected MongoTemplate template;

    @Override
    public boolean save(String collectionName, String json) {

      template.getCollection(collectionName).save(json);

      return true;
    }
}

Junit class,

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class MongoPersisterBeanTest {

    @InjectMocks
    private DocumentPersisterBean bean = new DocumentPersisterBean();

    @Mock
    @Autowired 
    private MongoTemplate mongoTemplate;

    @Before
    public void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    public void testSave() {

       System.out.println("Template "+mongoTemplate);

    System.out.println("Collection ===> "+mongoTemplate.getCollection("testCollection"));
    }

    @Configuration
    static class MongoTestConfiguration {

        @Bean
        public Mongo mongo() {
            // Configure a Fongo instance
            return new Fongo("mongo-test").getMongo();
        }

        @Bean
        public MongoTemplate mongoTemplate() {
            return new MongoTemplate(mongo(), "testDB");
        }

    }