@MockBean annotation in SpringBoot is not working

Question

I am trying to mock a service using @MockBean annotation, but I am getting the following error:

org.springframework.beans.factory.BeanCreationException: Could not inject field: FooService FooTest.fooService; nested exception is java.lang.IllegalStateException: FooService fooService cannot have an existing value

Here is the code sample I try with:

    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.boot.test.mock.mockito.MockBean;
    import org.springframework.test.context.junit4.SpringRunner;
        
    import FooService;
        
    @RunWith (SpringRunner.class)
    @SpringBootTest
    class FooTest {
        
    @Autowired
    FooService fooService;
    
    @MockBean
    BarService barService;
        
    @Test
    public void testMethod() throws Exception {
        
Mockito.doThrow(new ExceptionClass()).when(barService).externalWebSerivceCall();

//Verify @Retryable is calling 3 times
    
       }
    }
    
    class FooService {
        
    @Autowired
    BarService barService;
        
    @Retryable (value = ExceptionClass.class, maxAttempts = 3, backoff = @Backoff (delay = 3 * 60 * 1000))
    public void methodThatFails() {
        
       barService.externalWebSerivceCall();
        
    }


}

Any idea how I can resolve it?

Here is the entire stacktrace:

org.springframework.beans.factory.BeanCreationException: Could not inject field: FooService FooTest.fooService; nested exception is java.lang.IllegalStateException: The field FooService FooTest.fooService cannot have an existing value

    at org.springframework.boot.test.mock.mockito.MockitoPostProcessor.inject(MockitoPostProcessor.java:364)
    at org.springframework.boot.test.mock.mockito.MockitoPostProcessor.inject(MockitoPostProcessor.java:352)
    at org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener.lambda$injectFields$0(MockitoTestExecutionListener.java:79)
    at org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener.postProcessFields(MockitoTestExecutionListener.java:100)
    at org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener.injectFields(MockitoTestExecutionListener.java:79)
    at org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener.prepareTestInstance(MockitoTestExecutionListener.java:54)
    at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:244)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:227)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:289)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:291)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:246)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
    at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)
Caused by: java.lang.IllegalStateException: The field FooService FooTest.fooService cannot have an existing value
    at org.springframework.util.Assert.state(Assert.java:97)
    at org.springframework.boot.test.mock.mockito.MockitoPostProcessor.inject(MockitoPostProcessor.java:358)
    ... 27 more

Answer 1

I noticed that there is no @Serviceannotation on your Service class. One reason @MockBean might not be working is if you do not label the class as @Service or @Component.

If that’s not it, I’m not sure exactly why the @MockBean annotation is not working for you, but depending on what you are trying to test exactly you might want to use just @RunWith(SpringRunner.class) with an @TestConfiguration method and @Autowired for your Service instead of using @SpringBootTest on your class. This definitely works and would allow you to test the Service layer.

Here's an example that I've tested based on this article which says:

To check the Service class, we need to have an instance of the Service class created and available as a @Bean so that we can @Autowire it in our test class. We can achieve this configuration using the @TestConfiguration annotation.

During component scanning, we might find that components or configurations created only for specific tests accidentally get picked up everywhere. To help prevent this, Spring Boot provides the @TestConfiguration annotation that we can add on classes in src/test/java to indicate that they should not be picked up by scanning.

@RunWith(SpringRunner.class)
@DataJpaTest//good for working with JPA Components
// @SpringBootTest
class Tests {

    @TestConfiguration //tell spring that this configuration is only for testing environment
    static class UserDetailsServiceImplTextContext {
        @Bean //needed for creating instance for test autowiring
        public UserDetailsServiceImpl userDetailsServiceImpl() {
            return new UserDetailsServiceImpl();
        }
    }

    @Autowired
    private UserDetailsServiceImpl userServices;

    @Autowired
    TestEntityManager entityManager;

    @Test
    @DisplayName("Context Loads")
    void contextLoads() {
    }

    @Test
    @DisplayName("Create User")
    void createUser() {
        //given
        String a = "testUser";
        String email = "testUser@test.com";
        String username = a;
        String firstname = a;
        String lastname = a;
        String password = a;
        String userType = "USER";
        User u = new User(email, username, firstname, lastname, password, userType);
        //when
        entityManager.persist(u);
        entityManager.flush();
        //then
        User u2 = userServices.getUserRepo().findByUsername(username);
        //expect
        assertEquals(u, u2);
    }
}

Also here's another section of the article on the topic that might be helpful. It's an alternative example using @SpringBootTest showing the additional configuration involved.