junit test : java.lang.ClassCastException - unit-testing

Question

I am trying to implement junit testing with spring data jpa application. On controller level I am trying to implement unit testing. But I am getting Test failure class cast exception error.
DepartmentController.java
#RestController
#RequestMapping("/api.spacestudy.com/SpaceStudy/Control/SearchFilter")
public class DepartmentController {
#Autowired
DepartmentService depService;
#CrossOrigin(origins = "*")
#GetMapping("/loadDepartments")
public ResponseEntity<Set<Department>> findDepName() {
Set<Department> depname = depService.findDepName();
return ResponseEntity.ok(depname);
}
}
Junit test class
#RunWith(SpringRunner.class)
#WebMvcTest(DepartmentController.class)
public class SpaceStudyControlSearchFilterApplicationTests {
#Autowired
DepartmentController depController;
#Autowired
private MockMvc mockMvc;
#MockBean
DepartmentService depService;
#SuppressWarnings("unchecked")
Set<Department> mockDepartment = (Set<Department>) new Department(21629, "170330", "Administrative Computer");
#Test
public void findDepNameTest() throws Exception {
Mockito.when(depService.findDepName()).thenReturn( mockDepartment);
RequestBuilder requestBuilder = MockMvcRequestBuilders.get(
"/api.spacestudy.com/SpaceStudy/Control/SearchFilter/loadDepartments").accept(
MediaType.APPLICATION_JSON);
MvcResult result = mockMvc.perform(requestBuilder).andReturn();
System.out.println(result.getResponse());
String expected = "{nDeptId: 21629}";
JSONAssert.assertEquals(expected, result.getResponse().getContentAsString(), false);
}
}
Junit failure
java.lang.ClassCastException: com.spacestudy.model.Department cannot be cast to java.util.Set
at com.spacestudy.SpaceStudyControlSearchFilterApplicationTests.<init>(SpaceStudyControlSearchFilterApplicationTests.java:39)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
I am new to junit testing. Can any one tell me what I am doing wrong in test?

Answer 1

You are trying to cast a Department to Set<Department> at this line:
Set<Department> mockDepartment = (Set<Department>) new Department(21629, "170330", "Administrative Computer");
This cannot work. Instead you should create an empty set and then add the department, i.e. like this:
Set<Department> mockDepartment = new HashSet<Department>() {{
add(new Department(21629, "170330", "Administrative Computer"));
}};