NoSQLUnit MongoDB insert collection names are []

I am trying to write a JUnit test case for a Spring MongoDB Repository class in a Spring Boot project. But I keep getting the exception.

com.lordofthejars.nosqlunit.core.NoSqlAssertionError: Expected collection names are [student] but insert collection names are []

Any suggestions? Many thanks!

@Configuration
@EnableMongoRepositories
@ComponentScan("com.tp.repository")
public class TestConfig extends AbstractMongoConfiguration {

    @Bean
    public Mongo mongo() {
        return new Fongo("Fongo").getMongo();
    }

    @Bean
    protected String getDatabaseName() {
        return "test";
    }

}

Unit Test class

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = TestConfig.class)
public class StudentRepositoryTests {

    @Autowired
    StudentRepository studentRepository;

    @Autowired
    private ApplicationContext applicationContext;

    @Rule
    public MongoDbRule mongoDbRule = MongoDbRuleBuilder.newMongoDbRule()
            .defaultSpringMongoDb("student");

    @Test
    @ShouldMatchDataSet(location = "/student.json")
    public void shouldSave() {
        studentRepository.save(createStudent());
    }

    private Student createStudent() {
        Student student = new Student();
        student.setFirstName("First");
        student.setLastName("Last");
        return student;
    }

}

Student class

@Document(collection="student")
public class Student {

    @Id
    private String id;

    @Indexed
    private String firstName;

    @Indexed
    private String lastName;

    ....
}