@RunWith(SpringRunner.class) 
@SpringBootTest
public class DemoApplicationTests {
    private MockMvc mvc;
    @Before
    public void setUp() throws Exception {
        mvc = MockMvcBuilders.standaloneSetup(new HelloController()).build();
    }
    @Test
    public void getHello() throws Exception {
        mvc.perform(MockMvcRequestBuilders.get("/hello").accept(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk())
                .andExpect(content().string(equalTo("Hello World")));
    }
}