Overriding beans in Integration tests

@MockBean and bean overriding used by the OP are two complementary approaches.

You want to use @MockBean to create a mock and forget the real implementation : generally you do that for slice testing or integration testing that doesn't load some beans which class(es) you are testing depend on and that you don't want to test these beans in integration.
Spring makes them by default null, you will mock the minimal behavior for them to fulfill your test.

@WebMvcTest requires very often that strategy as you don't want to test the whole layers and @SpringBootTest may also require that if you specify only a subset of your beans configuration in the test configuration.

On the other hand, sometimes you want to perform an integration test with as many real components as possible, so you don't want to use @MockBean but you want to override slightly a behavior, a dependency or define a new scope for a bean, in this case, the approach to follow is bean overriding :

@SpringBootTest({"spring.main.allow-bean-definition-overriding=true"})
@Import(FooTest.OverrideBean.class)
public class FooTest{    

    @Test
    public void getFoo() throws Exception {
        // ...     
    }

    @TestConfiguration
    public static class OverrideBean {    

        // change the bean scope to SINGLETON
        @Bean
        @Scope(ConfigurableBeanFactory.SINGLETON)
        public Bar bar() {
             return new Bar();
        }

        // use a stub for a bean 
        @Bean
        public FooBar BarFoo() {
             return new BarFooStub();
        }

        // use a stub for the dependency of a bean 
        @Bean
        public FooBar fooBar() {
             return new FooBar(new StubDependency());
        }

    }
}

Since Spring Boot 1.4.x there is an option to use @MockBean annotation to fake Spring beans.

Reaction on comment:

To keep context in cache do not use @DirtiesContext, but use @ContextConfiguration(name = "contextWithFakeBean") and it will create separate context, while it will keep default context in cache. Spring will keep both (or how many contexts you have) in cache.

Our build is this way, where most of the tests are using default non-poluted config, but we have 4-5 tests that are faking beans. Default context is nicely reused

1. You can use @Primary annotation:

@Configuration
public class MockRestTemplateConfiguration {

    @Bean
    @Primary
    public RestTemplate restTemplate() {
        return Mockito.mock(RestTemplate.class)
    }
}

BTW, I wrote blog post about faking Spring bean

2. But I would suggest to take a look at Spring RestTemplate testing support. This would be simple example:

  private MockRestServiceServer mockServer;

  @Autowired
  private RestTemplate restTemplate;

  @Autowired
  private UsersClient usersClient;

  @BeforeMethod
  public void init() {
    mockServer = MockRestServiceServer.createServer(restTemplate);
  }

  @Test
  public void testSingleGet() throws Exception {
    // GIVEN
    int testingIdentifier = 0;
    mockServer.expect(requestTo(USERS_URL + "/" + testingIdentifier))
      .andExpect(method(HttpMethod.GET))
      .andRespond(withSuccess(TEST_RECORD0, MediaType.APPLICATION_JSON));


    // WHEN
    User user = usersClient.getUser(testingIdentifier);

    // THEN
    mockServer.verify();
    assertEquals(user.getName(), USER0_NAME);
    assertEquals(user.getEmail(), USER0_EMAIL);
  }

More examples can be found in my Github repo here

The Problem in your configuration is that you are using @Configuration for your test configuration. This will replace your main configuration. Instead use @TestConfiguration which will append (override) your main configuration.

46.3.2 Detecting Test Configuration

If you want to customize the primary configuration, you can use a nested @TestConfiguration class. Unlike a nested @Configuration class, which would be used instead of your application’s primary configuration, a nested @TestConfiguration class is used in addition to your application’s primary configuration.

Example using SpringBoot:

Main class

@SpringBootApplication() // Will scan for @Components and @Configs in package tree
public class Main{
}

Main config

@Configuration
public void AppConfig() { 
    // Define any beans
}

Test config

@TestConfiguration
public void AppTestConfig(){
    // override beans for testing
} 

Test class

@RunWith(SpringRunner.class)
@Import(AppTestConfig.class)
@SpringBootTest
public void AppTest() {
    // use @MockBean if you like
}

Note: Be aware, that all Beans will be created, even those that you override. Use @Profile if you wish not to instantiate a @Configuration.