Testing Spring Hateoas Application with RepresentationModelAssembler

Question

I'm trying to test my Spring Hateoas application, more specifically the controllers, using Springs @WebMvcTest. But I'm having problems injecting my custom RepresentationModelAssembler into the test.

First a bit of my setup: I'm using a custom RepresentationModelAssembler to turn my DB-Models into DTOs, which have all necessary links added.

The RepresentationModelAssembler:

@Component
public class BusinessUnitAssembler implements RepresentationModelAssembler<BusinessUnit, BusinessUnitDto> {

    private final Class<BusinessUnitController> controllerClass = BusinessUnitController.class;

    private final BusinessUnitMapper businessUnitMapper;

    public BusinessUnitAssembler(BusinessUnitMapper businessUnitMapper) {
        this.businessUnitMapper = businessUnitMapper;
    }

    @Override
    public BusinessUnitDto toModel(BusinessUnit entity) {
        return businessUnitMapper.businessUnitToDto(entity)
                .add(linkTo(methodOn(controllerClass).findById(entity.getId())).withSelfRel());
    }
}

The BusinessUnitMapper used here is a Mapstruct mapper, which is injected by spring. In my Service I use the BusinessUnitAssembler to turn my DB-Models into DTOs, example Service method:

public Page<BusinessUnitDto> findAll(Pageable pageable) {
    Page<BusinessUnit> pagedResult = businessUnitRepository.findAll(pageable);

    if (pagedResult.hasContent()) {
        return pagedResult.map(businessUnitAssembler::toModel);
    } else {
        return Page.empty();
    }
}

This is how I'm doing the testing currently:

@WebMvcTest(controllers = BusinessUnitController.class)
public class BusinessUnitControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private BusinessUnitService businessUnitService;

    private BusinessUnitMapper mapper = Mappers.getMapper(BusinessUnitMapper.class);
    private BusinessUnitAssembler assembler = new BusinessUnitAssembler(mapper);

    @Test
    public void getAllShouldReturnAllBusinessUnits() throws Exception {
        List<BusinessUnitDto> businessUnits = Stream.of(
                new BusinessUnit(1L, "Personal"),
                new BusinessUnit(2L, "IT")
        ).map(businessUnit -> assembler.toModel(businessUnit)).collect(Collectors.toList());
        when(businessUnitService.findAll(Pageable.ofSize(10))).thenReturn(new PageImpl<>(businessUnits));
        mockMvc.perform(get("/businessUnits").accept(MediaTypes.HAL_JSON))
                .andDo(print())
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.*", hasSize(3)))
                // ... do more jsonPath checking
    }
}

But I'd like to have Spring inject the BusinessUnitAssembler, instead of constructing it myself. I've tried @Importing BusinessUnitAssembler as well as the BusinessUnitMapper and I've also tried it by using a custom @Configuration but I just couldn't get it to work.

So my Question is: How can I let Spring inject my BusinessUnitAssembler into the test for me instead of assembling it myself?

Additional Question: Is it valid to combine the Mapping from Database Entity to DTO in the RepresentationModelAssembler or should those two steps be kept seperate from each other?