Rest Spring Boot mockmvc测试When（）thenReturn（）存根返回Null

我正在编写一个单元测试来测试RESTAPI端点。我使用mockmvc处理API测试，使用@injectmock加载端点，使用@mock模拟服务层。下面是一些片段

测试类

@RunWith(SpringRunner.class)
@SpringBootTest
public class CurrencyConverterControllerTest {

    private MockMvc mockMvc;

    @InjectMocks
    private CurrencyConverterController controller;

    @Mock
    private CurrencyConverterService cs;

    @Before
    public void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
        mockMvc = MockMvcBuilders.standaloneSetup(controller).build();
    }

    @Test
    public void statusCheckTest() throws Exception {
        SendingResponseDTO dto = new SendingResponseDTO();
        String source = "GBP";
        String target = "USD";
        Double number = 32.56;
        dto.setSourceCurrency(source);
        dto.setTargetCurrency(target);
        dto.setNumber(number);
        dto.setTargetCurrencyValue(1.3136300664);
        dto.setTotalValue("$42.77");

        String apiURL = "/currency/converter/" + source + "/" + target + "/" + number;
        Mockito.when(cs.convertService(source, target, number)).thenReturn(dto);
        MvcResult result = mockMvc.perform(get(apiURL).contentType(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk()).andDo(print()).andReturn();
    }

@RestController
@RequestMapping("/currency")
@Validated
public class CurrencyConverterController {
    @Autowired
    CurrencyConverterService converterService;

    @Traceable
    @GetMapping(value = "/converter/{source}/{target}/{number}")
    public ResponseEntity<SendingResponseDTO> convertCurrency(
            @PathVariable("source") @CurrencyValidator @Pattern(regexp = "[a-zA-Z]{3}") @NotBlank @Size(min = 3) String source,
            @PathVariable("target") @CurrencyValidator @Pattern(regexp = "[a-zA-Z]{3}") @NotBlank @Size(min = 3) String target,
            @PathVariable("number") Double number) throws NotFoundException, InputsShouldNotBeSameException {

        if (source.equals(target)) {
            throw new InputsShouldNotBeSameException(
                    " Source Currency and Target currency should not be same for the conversion.");
        }
        SendingResponseDTO val = converterService.convertService(source.toUpperCase(), target.toUpperCase(), number);
        return ResponseEntity.ok().body(val);
    }
}

控制器类

@RunWith(SpringRunner.class)
@SpringBootTest
public class CurrencyConverterControllerTest {

    private MockMvc mockMvc;

    @InjectMocks
    private CurrencyConverterController controller;

    @Mock
    private CurrencyConverterService cs;

    @Before
    public void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
        mockMvc = MockMvcBuilders.standaloneSetup(controller).build();
    }

    @Test
    public void statusCheckTest() throws Exception {
        SendingResponseDTO dto = new SendingResponseDTO();
        String source = "GBP";
        String target = "USD";
        Double number = 32.56;
        dto.setSourceCurrency(source);
        dto.setTargetCurrency(target);
        dto.setNumber(number);
        dto.setTargetCurrencyValue(1.3136300664);
        dto.setTotalValue("$42.77");

        String apiURL = "/currency/converter/" + source + "/" + target + "/" + number;
        Mockito.when(cs.convertService(source, target, number)).thenReturn(dto);
        MvcResult result = mockMvc.perform(get(apiURL).contentType(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk()).andDo(print()).andReturn();
    }

@RestController
@RequestMapping("/currency")
@Validated
public class CurrencyConverterController {
    @Autowired
    CurrencyConverterService converterService;

    @Traceable
    @GetMapping(value = "/converter/{source}/{target}/{number}")
    public ResponseEntity<SendingResponseDTO> convertCurrency(
            @PathVariable("source") @CurrencyValidator @Pattern(regexp = "[a-zA-Z]{3}") @NotBlank @Size(min = 3) String source,
            @PathVariable("target") @CurrencyValidator @Pattern(regexp = "[a-zA-Z]{3}") @NotBlank @Size(min = 3) String target,
            @PathVariable("number") Double number) throws NotFoundException, InputsShouldNotBeSameException {

        if (source.equals(target)) {
            throw new InputsShouldNotBeSameException(
                    " Source Currency and Target currency should not be same for the conversion.");
        }
        SendingResponseDTO val = converterService.convertService(source.toUpperCase(), target.toUpperCase(), number);
        return ResponseEntity.ok().body(val);
    }
}

@RestController
@请求映射（“/currency”）
@验证
公共类CurrencyConverterController{
@自动连线
货币兑换服务兑换服务；
@可追溯
@GetMapping（value=“/converter/{source}/{target}/{number}”）
公共责任与货币(
@PathVariable（“source”）@CurrencyValidator@Pattern（regexp=“[a-zA-Z]{3}”）@NotBlank@Size（min=3）字符串源，
@PathVariable（“target”）@CurrencyValidator@Pattern（regexp=“[a-zA-Z]{3}”）@NotBlank@Size（min=3）字符串目标，
@PathVariable（“数字”）双倍数字）引发NotFoundException，InputsShouldNotBeSameException{
if（源等于（目标））{
抛出新输入shouldnotbesameeexception(
“转换时，源货币和目标货币不应相同。”）；
}
sendingressponsedto val=converterService.convertService（source.toUpperCase（），target.toUpperCase（），number）；
返回ResponseEntity.ok（）.body（val）；
}
}

这里的问题是

Mockito.when（cs.convertService（source，target，number）），然后返回（dto）
不返回所需的DTO，而是返回null

关于如何处理这个问题有什么建议吗
 尝试
Mockito.when（cs.convertService（Mockito.anyString（），Mockito.anyString（），Mockito.anyDouble（））。然后返回（dto）；
@AlanHay，非常感谢。这就像一个符咒：）确保在模拟调用中放入任何内容时使用模拟对象作为参数。