Spring Testing - WebTestClient Could not autowire. No beans of 'WebTestClient' type found

I want to use WebTestClient in my tests. works like this:

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@AutoConfigureWebTestClient
public class ControllerTest {

    @Autowired
    private WebTestClient webTestClient;

    @Test
    public void webtestClient () {
        assertNotNull(webTestClient);
    }
}

But now I want to inject WebTestClient into a helper class:

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@AutoConfigureWebTestClient
public class ControllerTest {

    @Autowired
    private Helper helper;

    @Test
    public void webtestClient () {
        helper.check();
    }
}

@Component
public class Helper {
    @Autowired
    private WebTestClient webTestClient;

    public void check() {
        assertNotNull(webTestClient);
    }
}

Works, too. But Intellij is showing an error:

Could not autowire. No beans of 'WebTestClient' type found. more... (Strg+F1)

How can I fix this?