How to mock RestTemplate in Springboot app

Question

This question has already been asked. The accepted answer doesn't work for me. Here is my code:-

My service is here:

@Service
public class PlantService {

    @Autowired
    RestTemplate restTemplate;

    static String url = "http://some_url_?Combined_Name=Oak";

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        return builder.build();
    }

    public String getJson() {
        ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);
        return response.getBody();
    }
}

My unit test

@RunWith(SpringRunner.class)
class PlantServiceTest {

    private PlantService plantService;
    @Mock
    @Autowired
    private RestTemplate restTemplate;

    @Before
    void setUp() {
        MockitoAnnotations.initMocks(this);
        plantService = new PlantService();
    }

    @Test
    void testGetJsonString() {
        // arrange
        String expectedJson = "Some json string";
        ResponseEntity mocResponse = mock(ResponseEntity.class);

        // act
        when(restTemplate.getForEntity("url", String.class)).thenReturn(mocResponse);
        String actualJson = plantService.getJson();
        // assert
        assertSame(expectedJson, actualJson);
    }
}

When I debug and step into the actual code. I can see restTemplate is null and throws java.lang.NullPointerException. So how do I unit test this code?

Answer 1

I have tried your code running on my machine.

Please find the test running test class

@RunWith(SpringRunner.class)
class PlantServiceTest {

    @InjectMocks
    private PlantService plantService;

    @Mock
    private RestTemplate restTemplate;

    String url = "http://some_url_?Combined_Name=Oak";

    @BeforeEach
    void setUp() {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    void testGetJsonString() {
        // arrange
        String expectedJson = "Some json string";
        ResponseEntity mocResponse = new ResponseEntity("Some json string", HttpStatus.OK);

        // act
        when(restTemplate.getForEntity(url, String.class)).thenReturn(mocResponse);
        String actualJson = plantService.getJson();
        // assert
        assertSame(expectedJson, actualJson);
    }
}