<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

@Service
public class HelloWorldService {
    public void sayHello() {
        System.out.println("Hello world");
    }
}

@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest(classes = App.class)
public class HelloWorldServiceTest {

    @Autowired
    private HelloWorldService helloWorldService;

    @Test
    public void sayHello() throws Exception {
        helloWorldService.sayHello();
    }

}