@Import vs @ContextConfiguration for importing beans in unit tests

Question

I was able to set up and successfully run three different test configurations with SpringBoot 1.5.3

Method #1. Importing Bean with use of @Import annotation

@RunWith(SpringJUnit4ClassRunner.class)
@Import({MyBean.class})
public class MyBeanTest() {
    @Autowired
    private MyBean myBean;
}

Method #2. Importing Bean with use of @ContextConfiguration annotation

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {MyBean.class})
public class MyBeanTest() {
    @Autowired
    private MyBean myBean;
}

Method #3 (with internal class configuration; based on the official blog post)

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(loader=AnnotationConfigContextLoader.class)
public class MyBeanTest() {

    @Configuration
    static class ContextConfiguration {
        @Bean
        public MyBean myBean() {
            return new MyBean();
        }
    }

    @Autowired
    private MyBean myBean;

}

Taking into account @Import annotation documentation

Indicates one or more {@link Configuration @Configuration} classes to import.

and the fact that MyBean is not a configuration class, but a bean class annotated with @Component annotation it looks like Method #1 is not correct.

From @ContextConfiguration documentation

{@code @ContextConfiguration} defines class-level metadata that is used to determine how to load and configure an {@link org.springframework.context.ApplicationContext ApplicationContext} for integration tests.

Sounds like it is better applicable to unit tests, but still, should load a kind of a configuration.

Methods #1 and #2 are shorter and simpler. Method #3 looks like a correct way.

Am I right? Are there other criteria why I should use method #3, like performance or something else?

Answer 1

You actually don't need to specify the loader if you go with option #3. From the doc In addition to the example from the doc you can override the env. with @TestPropertySource if you need to inject properties in the environment without using the real ones.

@RunWith(SpringRunner.class)
// ApplicationContext will be loaded from the
// static nested Config class
@ContextConfiguration
@TestPropertySource(properties = { "timezone = GMT", "port: 4242" })
public class OrderServiceTest {

    @Configuration
    static class Config {

        // this bean will be injected into the OrderServiceTest class
        @Bean
        public OrderService orderService() {
            OrderService orderService = new OrderServiceImpl();
            // set properties, etc.
            return orderService;
        }
    }

    @Autowired
    private OrderService orderService;

    @Test
    public void testOrderService() {
        // test the orderService
    }

}