Java Spring dependency injection not working

I am very new to Java Spring and I tried to set up 2 classes and a Test for one of them. That is my project structure:

Here is the code for the classes:

<!-- language: java -->

@Component
public class Box {
    private Item item;
    @Autowired
    public Box(Item item) {
        this.item = item;
    }
    public Item getItem() {
        return item;
    }
}

<!-- language: java -->

@Configuration
@ComponentScan
public class BoxConfig {}

<!-- language: java -->

@Component
public class Item {}

And here is the code of the JUnit Test I wrote in the BoxTest class:
<!-- language: java -->

@ContextConfiguration(classes = {BoxConfig.class})
public class BoxTest {
    @Autowired
    Box box;
    @Test
    public void BoxTest1() {
        Assertions.assertNotNull(box.getItem());
    }
}

My Expectation was, that Spring automatically injects a box object into the box attribute of the Test, but the box attribute ist always null so I keep getting a NullReferenceException. Does someone know why it is not properly initialised?

BoxTest needs to be included in Spring configuration somehow.
E.g. using @ExtendWith(SpringExtension.class) would help.

You can look at other options in Spring documentation.