How to mock RestTemplate in Springboot app - spring-boot

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);
}
}

Answer 2

You can do the following:
Remove #RunWith annotation.
Annontate your test class with #RestClientTest from org.springframework.boot.test.autoconfigure.web.client.RestClientTest.
Use MockRestServiceServer from org.springframework.test.web.client.MockRestServiceServer.
Mock the response of the server when being called in the test method, example:
#RestClientTest
public class MyTest {
#Autowired
private MockRestServiceServer server;
public void test() {
// setup
String expected = "test_value";
server.expect(requestToUriTemplate("/myendpoint"))
.andRespond(withSuccess(myJsonResponse, MediaType.APPLICATION_JSON));
// act
String actual = myClient.fetch(myRequestDto);
// assert
assertThat(actual, equalTo(expected));
server.verify();
}
}
I'm using assertThat from hamcrest, you can use whatever you want to assert the correctness of the result.

Answer 3

You should use constructor injection in your PlantService. For instance:
public class PlantService {
RestTemplate restTemplate;
#Autowired
public PlantService(RestTemplate restTemplate){
this.restTemplate = restTemplate;
}
}
And on your test you can just do:
plantService = new PlantService(restTemplate);
^^
yourMock

Answer 4

Your problem is the plantService = new PlantService(); You never inject into this selft created instance.
Solution 1
I usually do it like this:
#InjectMocks
private PlantService plantService = new PlantService();
#Mock
private RestTemplate restTemplate;
Remove the setup method and run with Mockito instead of the SpringRunner.
Solution 2
If you need the SpringRunner you can do the following:
#BeforeEach
void setUp() {
MockitoAnnotations.initMocks(this);
plantService = new PlantService();
ReflectionTestUtils.setField(plantService, "restTemplate", restTemplate);
}
As I've worked with JUnit 5 in the last years, I'm not sure about the SpringRunner. In JUnit 5 I can use both extensions (Spring and Mockito at the same time). Maybe this also worked in JUnit 4.