Unit Test API REST Spring

I would like to do some unit tests for my API REST (Spring Boot App)

I have been reading this: http://ift.tt/19VZzPU

I have made my first test:

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration public class LogInTest {

private MockMvc mockMvc;

//Add WebApplicationContext field here.

//The setUp() method is omitted.

@Test
public void findAll_TodosFound_ShouldReturnFoundTodoEntries() throws Exception {

    mockMvc.perform(get("/logIn?name=dani&encrypted=81dc9bdb52d04dc20036dbd8313ed055"))
            .andExpect(status().isOk())
            .andExpect(content().contentType(TestUtil.APPLICATION_JSON_UTF8))
            .andExpect(jsonPath("$", hasSize(2)))
            .andExpect(jsonPath("$[0].status", is(1)))
            .andExpect(jsonPath("$[0].error", is("")))
            .andExpect(jsonPath("$[0].data", is("OK")));
}

}

When I run the test as JUnit test I get the following error: java.lang.IllegalStateException: Failed to load ApplicationContext

I don't know how to add - WebApplicationContext field here - setUp() method

Can someone give me an example of WebApplicationContext and setUp() method?

Thanks