ReflectionTestUtils - Setting field of type [null] on target object

Question

I am new with Unit testing and Mockito. I'm trying to write tests for my Dao class:

@Repository
@NoArgsConstructor
public class UserDaoImpl implements UserDao {
    
    private NamedParameterJdbcTemplate template;
    
    @Value("${users.find.by_id}")
    private String findByIdQuery;
    
    private RowMapper<User> rowMapper = (rs, rowNum) -> {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setFirstName(rs.getString("firstname"));
        user.setLastName(rs.getString("lastname"));
        user.setEmail(rs.getString("email"));
        user.setPassword(rs.getString("password"));
        user.setEnabled(rs.getBoolean("enabled"));
        return user;
    };

    public UserDaoImpl(NamedParameterJdbcTemplate template) {
        super();
        this.template = template;
    }

    @Override
    public Optional<User> findById(int id) {
        SqlParameterSource param = new MapSqlParameterSource("id", id);
        User user = null;
        try {
            user = template.queryForObject(findByIdQuery, param, BeanPropertyRowMapper.newInstance(User.class));
        } catch (DataAccessException ex) {
            ex.printStackTrace();
        }
        return Optional.ofNullable(user);
    }
}

In my simple test I simply added @Mock anotation for my NamedParameterJdbcTemplate , and trying to put it into the UserDaoImpl :

public class UserDaoTest {
    
    @Mock
    public NamedParameterJdbcTemplate template;
    @InjectMocks
    public UserDao userDao;
    
    @Test
    public void findByIdTest() {
        template = new NamedParameterJdbcTemplate(new EmbeddedDatabaseBuilder()
                .setType(EmbeddedDatabaseType.H2)
                .addScript("classpath:db/schema.sql")
                .addScript("classpath:db/test-data.sql")
                .build());
        userDao = new UserDaoImpl();
        ReflectionTestUtils.setField(userDao, "template", template);
        Mockito.when(userDao.findById(1).get().getEmail()).thenReturn("Keanu@gmail.com");
        
        User user = userDao.findById(1).get();
        assertNotNull(user);
        assertEquals("Keanu@gmail.com", user.getEmail());
    }
}

Each time I run the test, I get java.lang.NullPointerException for the field template . Cant find what is the correct way of implementing the test.

Answer 1

The problem is that you are missing the enablement of Mockito annotations in your test. In order to achieve this, you need to either use @RunWith(MockitoJUnitRunner.class) in your test class as follows:

@RunWith(MockitoJUnitRunner.class)
public class UserDaoTest {
    (...)
}

Or you enable Mockito annotations programmatically:

public class UserDaoTest {
    
    @Mock
    public NamedParameterJdbcTemplate template;
    
    @InjectMocks
    public UserDao userDao;

    @Before
    public void init() {
        MockitoAnnotations.initMocks(this);
    }
    
    @Test
    public void findByIdTest() {
        template = new NamedParameterJdbcTemplate(new EmbeddedDatabaseBuilder()
                .setType(EmbeddedDatabaseType.H2)
                .addScript("classpath:db/schema.sql")
                .addScript("classpath:db/test-data.sql")
                .build());
        userDao = new UserDaoImpl();
        ReflectionTestUtils.setField(userDao, "template", template);
        Mockito.when(userDao.findById(1).get().getEmail()).thenReturn("Keanu@gmail.com");
        
        User user = userDao.findById(1).get();
        assertNotNull(user);
        assertEquals("Keanu@gmail.com", user.getEmail());
    }
}