Testing a REST endpoint with Spring, MongoDB using ObjectIds - spring

Question

I'm new to MongoDB and I'm writing a series of unit tests for a Mongo-backed REST web-service. Here's a simple test for a /clients/{id} enpoint :
#RunWith(MockitoJUnitRunner.class)
public class ClientsControllerMockMvcStandaloneTest {
private MockMvc mvc;
#Mock
private ClientsRepository clientsRepository;
#Mock
private ModelMapper modelMapper;
#InjectMocks
private ClientsController clientsController;
private ExceptionHandlerExceptionResolver createExceptionResolver() {
ExceptionHandlerExceptionResolver exceptionResolver = new ExceptionHandlerExceptionResolver() {
#SuppressWarnings("ConstantConditions")
#Override
protected ServletInvocableHandlerMethod getExceptionHandlerMethod(final HandlerMethod handlerMethod,
final Exception exception) {
final Method method = new ExceptionHandlerMethodResolver(RestResponseEntityExceptionHandler.class)
.resolveMethod(exception);
final RestResponseEntityExceptionHandler handler = new RestResponseEntityExceptionHandler();
return new ServletInvocableHandlerMethod(handler, method);
}
};
exceptionResolver.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
exceptionResolver.afterPropertiesSet();
return exceptionResolver;
}
#Before
public void setup() {
JacksonTester.initFields(this, new ObjectMapper());
mvc = MockMvcBuilders.standaloneSetup(clientsController)
.setHandlerExceptionResolvers(createExceptionResolver())
.build();
}
// GET /api/clients/{id} 200
#Test
public void findById_ClientEntryFound_ShouldReturnFoundClientEntry() throws Exception {
final ObjectId id = new ObjectId();
final Client client = Client.builder()
.id(id)
.name("Microsoft")
.build();
final ClientDTO clientDTO = ClientDTO.builder()
.id(id)
.name("Microsoft")
.build();
when(clientsRepository.findById(id))
.thenReturn(Optional.of(client));
when(modelMapper.map(client, ClientDTO.class))
.thenReturn(clientDTO);
mvc.perform(get("/clients/" + id.toString())
.accept(TestUtils.APPLICATION_JSON_UTF8))
.andExpect(content().contentType(TestUtils.APPLICATION_JSON_UTF8))
.andExpect(status().isOk())
.andExpect(jsonPath("$.id", is(id)))
.andExpect(jsonPath("$.name", is("Microsoft")))
.andDo(MockMvcResultHandlers.print());
verify(modelMapper, times(1)).map(client, ClientDTO.class);
verify(clientsRepository, times(1)).findById(id);
verifyNoMoreInteractions(clientsRepository);
}
}
I expect this to work but I'm getting the following :
java.lang.AssertionError: JSON path "$.id"
Expected: is <5c9b9a0289d2b311b150b92c>
but: was <{timestamp=1553701378, machineIdentifier=9032371, processIdentifier=4529, counter=5290284, timeSecond=1553701378, time=1553701378000, date=1553701378000}>
Expected :is <5c9b9a0289d2b311b150b92c>
Actual :<{timestamp=1553701378, machineIdentifier=9032371, processIdentifier=4529, counter=5290284, timeSecond=1553701378, time=1553701378000, date=1553701378000}>
<Click to see difference>
Any help would be appreciated (including any pointers if you think my general approach could be improved!).
Cheers!

Answer 1

Jackson doesn't know your ObjectId instance should be serialized as 5c9b9a0289d2b311b150b92c and not as:
{
"timestamp": 1553701378,
"machineIdentifier": 9032371,
"processIdentifier": 4529,
"counter": 5290284,
"time": 1553701378000,
"date": 1553701378000,
"timeSecond": 1553701378
}
Luckily it's easy to fix. The ObjectId#toString() method (which will internally invoke ObjectId#toHexString()) allows you to convert the ObjectId instance into a 24-byte hexadecimal string representation.
So you could use #JsonSerialize along with ToStringSerializer to have the ObjectId instance represented as a string:
#JsonSerialize(using = ToStringSerializer.class)
private ObjectId id;
Then, in your test, use the ObjectId#toString() method (or ObjectId#toHexString()) for the assertion:
.andExpect(jsonPath("$.id", is(id.toString())))
Alternatively, assuming that you are using Spring Data for MongoDB, instead of ObjectId, you could use:
#Id
private String id;
You also could handle the conversion of ObjectId to String in your mapper layer.