[FIXED] JUnit POST @Test returns empty string

Issue

Problem

I'm trying to write a test for a Spring controller but the test itself doesn't seem to return anything. What's odd is that if I manually test this with Postman I get the expected results.

Expecting

What I'm expecting

{
  "title": "My Third Todo"
}

Postman

What I'm getting (empty response?)

Relevant Code

TodoService

@Service
public class TodoService {

    private TodoRepository todoRepository;

    @Autowired
    public TodoService(TodoRepository todoRepository) {
        this.todoRepository = todoRepository;
    }

    public List<Todo> findAll() {
        return todoRepository.findAll();
    }

    public Todo findById(Long todoId) {
        return todoRepository.findById(todoId).orElse(null);
    }

    public Todo save(Todo todo) {
        return todoRepository.save(todo);
    }

    public void deleteById(Long todoId) {
        todoRepository.deleteById(todoId);
    }

}

TodoController

@RestController
@RequestMapping("/api/todos")
public class TodoController {

    private TodoService todoService;

    @Autowired
    public TodoController(TodoService todoService) {
        this.todoService = todoService;
    }

    @PostMapping
    public Todo save(@RequestBody Todo todo) {
        return todoService.save(todo);
    }

}

TodoControllerTest

@RunWith(SpringRunner.class)
@WebMvcTest(TodoController.class)
public class TodoControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private TodoService todoService;

    private List<Todo> todos;

    public TodoControllerTest() {
        Todo firstTodo = new Todo();
        firstTodo.setId(1L);
        firstTodo.setTitle("My First Todo");

        Todo secondTodo = new Todo();
        secondTodo.setId(2L);
        secondTodo.setTitle("My Second Todo");

        todos = new ArrayList<>();
        todos.add(firstTodo);
        todos.add(secondTodo);
    }

    @Test
    public void save() throws Exception {
        Todo thirdTodo = new Todo();
        thirdTodo.setId(3L);
        thirdTodo.setTitle("My Third Todo");

        when(todoService.save(thirdTodo)).thenReturn(thirdTodo);

        String mock = mockMvc.perform(post("/api/todos")
                .contentType(MediaType.APPLICATION_JSON)
                .content("{\"title\": \"My Third Todo\"}"))

                .andExpect(status().isOk())

                .andReturn()
                .getResponse()
                .getContentAsString();

        System.out.println("\n\n\n");
        System.out.println("Mock: " + mock);
        System.out.println("\n\n\n");
    }

}

Solution

It appears that when sending up JSON in a POST request you need to have a 1:1 mapping of the object that your JSON represents. In my above example in my @Test I did not do this.

Example Class

public class MyObject {
    private Long id;
    private String title;

    // Constructor, getters, and setters
}

With the example class my MyObject, when you want to pass this to RequestBuilder.post(...).content(...) you apparently need to have that 1:1 mapping like so

RequestBuilder.post(...)
  content("{\"id\":1,\"title\":\"My Third Todo\"}\")

Another suggestion is to use ObjectMapper to convert an object to JSON.

Todo todo = new Todo(1L, "My Third Todo");
ObjectMapper mapper = new ObjectMapper();

String todoJson = mapper.writeValueAsString(todo);

mockMvc.perform(RequestBuilder.post("/api/todos")
                .contentType(MediaType.APPLICATION_JSON)
                .content(todoJson))
    // do whatever else you need

Answered By - Brandon Benefield