How can I mock the service class in my Controller Test in Micronaut using JUnit5?

Question

I am writing a JUnit test case for the controller in my micronaut application. The controller has a GET endpoint which invokes a method in my service class. I am getting a NullPointerException so I am assuming that my service class might not be properly mocked however, I am not sure. I am using @Mock (Mockito) for the service.

Am I using the correct annotation to mock the service layer? I have tried to search on google but it hasn't given me much to look into. Thanks.

@MicronautTest
public class FPlanControllerTest {

private static final String url = "dummy_url";

@Inject
FPlanService fplanService;

@Inject
@Client("/")
RxHttpClient client;

@Test
public void testGetLayout() {
    FPlanUrl expectedFPlanUrl = new FPlanUrl(url);
    when(fplanService.getLayoutUrl(Mockito.anyString(), Mockito.anyString()))
                .thenReturn(expectedFPlanUrl);
        FPlanUrl actualFPlanUrl = client.toBlocking()
                .retrieve(HttpRequest.GET("/layout/1000545").header("layoutId", "7"), FPlanUrl.class);
        assertEquals(expectedFPlanUrl , actualFPlanUrl);
    }

@MockBean(FPlanService.class)
    FPlanService fplanService() {
        return mock(FPlanService.class);
    }
}

I received the below error.

java.lang.NullPointerException at com.apartment.controller.FPlanControllerTest.testGetLayout(FPlanControllerTest.java:44)

Answer 1

I figured out what went wrong. This was giving a NullPointerException because the HTTP response was expecting a String and not the FPlanUrl object. The correct code is as below:

@Test
public void testGetLayout() {
    FPlanUrl expectedFPlanUrl = new FPlanUrl("http://dummyurl.com");
    when(fplanService.getLayoutUrl(Mockito.anyString(), Mockito.anyString()))
            .thenReturn(expectedFPlanUrl);
    Assertions.assertEquals("{\"url\":\"http://dummyurl.com\"}", client.toBlocking().retrieve(HttpRequest.GET("/layout/123").header("layoutId", "7"), String.class);
    verify(fplanService).getLayoutUrl("123","7");
}