问NullPointerException: Junit Spring注解配置

EN

import javax.annotation.Nonnull;

public class UkrainianSongs implements CompactDisk{
    @Override
    @Nonnull
    public String getTitle(){
        return "Ukranian Songs";
    }

    @Override
    @Nonnull
    public String getArtist(){
        return "Skriabin";
    }
}

@Configuration
@ComponentScan
public class CDPlayerConfig {

    @Bean
    public CompactDisk anUkranianDisk(){
        return  new UkrainianSongs();
    }
}

@Component
public class CompactDiskBox {

    @Autowired
    public CompactDisk anUkrainianDisk;
} 

@RunWith(JUnit4.class)
@ContextConfiguration(classes = CDPlayerConfig.class)
public class CompactDiskBoxTest {
    @Autowired(required = true)
    public CompactDiskBox compactDiskBox;

    @Test
    public void testUkranianDisk(){
        assertNotNull(compactDiskBox.anUkrainianDisk);
    }
}