Mockmvc returns empty response body even if response status is 200 - spring-boot

Question

I am trying to learn Junit and I ended up in a situation where my testcase returns 200 status code but returns null response Body. Its just a simple save operation using JPA repo and I have tried many online solutions but none worked for me.
Testclass :
#RunWith(SpringRunner.class)
#SpringBootTest
#AutoConfigureMockMvc
class CarManufacturingSystemApplicationTests {
#Autowired
private MockMvc mockMvc;
#MockBean
private GroupController groupController;
ObjectMapper om = new ObjectMapper();
#Test
public void createGroupTest() throws Exception {
GroupCreateRequest createRequest = new GroupCreateRequest();
createRequest.setActiveFlag(true);
createRequest.setGroupName("test");
createRequest.setPlantCode(1L);
String expectedjson = "{\r\n" + "\"message\": \"Group created successfully\"\r\n" + "}";
MvcResult result = mockMvc.perform(post("/group/createGroup")
.contentType(MediaType.APPLICATION_JSON_VALUE).accept(MediaType.APPLICATION_JSON_VALUE).content(new Gson().toJson(createRequest)))
.andExpect(status().isOk())
.andReturn();
String actualJson = result.getResponse().getContentAsString();
Assert.assertEquals(expectedjson, actualJson);
}
Controller:
#RestController
#RequestMapping(value = "/group")
public class GroupController {
#Autowired
private GroupService groupService;
#PostMapping("/createGroup")
public ResponseEntity<Response> createGroup(#RequestBody GroupCreateRequest groupCreateRequest) {
Response response = groupService.createGroup(groupCreateRequest);
return new ResponseEntity<> (response, HttpStatus.OK);
}
}
Error:
org.junit.ComparisonFailure: expected:<[{
"message": "Group created successfully"
}]> but was:<[]>
at org.junit.Assert.assertEquals(Assert.java:115)
at org.junit.Assert.assertEquals(Assert.java:144)
at com.nissan.car.manufacturing.system.CarManufacturingSystemApplicationTests.createGroupTest(CarManufacturingSystemApplicationTests.java:87)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
Service implementation
public Response createGroup(GroupCreateRequest groupCreateRequest) {
Group group = new Group();
Response response = new Response();
try {
addGroupDetails(groupCreateRequest, group);
groupRepository.save(group);

Answer 1

Note that your are testing GroupController, not GroupService, so you should mock the GroupService. Please replace
#MockBean
private GroupController groupController;
to
#MockBean
private GroupService groupService;
And then using simple stubbing directives when(something).thenReturn(somethingElse) to make your groupService return the response you specified.
#Test
public void createGroupTest() throws Exception {
// ...
Response response = new Response();
response.setMessage("Group created successfully");
when(groupService.createGroup(any())).thenReturn(response);
// ...
Assert.assertEquals(expectedjson, actualJson);
}