How to get nested objects inside entity - spring-boot

Question

I'm new with unit tests. I'm trying test Service Layer in a SPRING APP.
Good, i have any relationships in my Service.
VirtualDatacenterModel vdc = vdcRepository.findById(vmDTO.getVdc()).orElseThrow(() -> new ClientException("Invalid VDC id"));
DataCenterModel dc = vdc.getDatacenter();
String vmName = vdc.getTenant().getName() + "_[" + vmDTO.getName() + "]";
In my test i used MOCKITO, dependencies already is mocked, then i cannot see where is wrong
CreateVmDTO vmDTO = Mockito.mock(CreateVmDTO.class);
VmModel vm = Mockito.mock(VmModel.class);
VirtualDatacenterModel vdc = Mockito.mock(VirtualDatacenterModel.class, Mockito.RETURNS_DEEP_STUBS);
TenantModel tenant = Mockito.mock(TenantModel.class);
Mockito.when(vmRepository.save(vm)).thenReturn(new VmModel());
Mockito.when(vdcRepository.findById(vmDTO.getVdc())).thenReturn(Optional.of(new VirtualDatacenterModel()));
Mockito.doReturn(tenant).when(vdc).getTenant();
Mockito.when(vdc.getTenant().getName()).thenReturn("Olivia");
VmModel vmReturn = vmService.createVM(vmDTO);
And i receive NullPointerException, i probably don't know how to use Mockito correctly

Answer 1

You can only mock one action at the time, the following line will certainly be a problem:
Mockito.when(vdcRepository.findById(vmDTO.getVdc())).thenReturn(Optional.of(new VirtualDatacenterModel()));
cause vmDTO.getVdc() will return a null pointer. (vmDTO is a mocked object itself, and has no instruction set for that call). Assuming vmDTO.getVdc() returns the vdc, you can fix as follows:
CreateVmDTO vmDTO = Mockito.mock(CreateVmDTO.class);
VmModel vm = Mockito.mock(VmModel.class);
VirtualDatacenterModel vdc = Mockito.mock(VirtualDatacenterModel.class, Mockito.RETURNS_DEEP_STUBS);
//example fix:
Mockito.when(vmDTO.getVdc()).thenReturn(vdc);
TenantModel tenant = Mockito.mock(TenantModel.class);
Mockito.when(vmRepository.save(vm)).thenReturn(new VmModel());
//also you can do directly:
Mockito.when(vdcRepository.findById(vdc)).thenReturn(Optional.of(new VirtualDatacenterModel()));
Mockito.doReturn(tenant).when(vdc).getTenant();
Mockito.when(vdc.getTenant().getName()).thenReturn("Olivia");
VmModel vmReturn = vmService.createVM(vmDTO);
Also the naming of your methods throws me off:
You have a method vdcRepository.findById, but your input is a vdc object, and not an id? Either the naming is confusing or your input is wrong. If getVdc returns an Id, then you can fix the code by mocking the return of an Id (rename the method to getVdcId or something).
Note: Personally, I seldom mock a DTO. It is just as easy to make the real DTO object, since they often come with a builder or getter/setter.