Mockito.when返回Null问题：CrossSellOffersServiceAdapter测试异常

看起来你遇到的Mock返回null问题，主要是由Mock对象类型不匹配和测试参数顺序错误这两个核心问题导致的，我帮你拆解并给出修复方案：

1. 最关键的问题：Mock对象类型不匹配 #

你的CrossSellOffersServiceAdapter类中注入的依赖是CrossSellOffersConnectBDS类型，但在测试类里Mock的却是CrossSellOffersConnectBDSAdapter类型。Mockito无法将错误类型的Mock对象注入到目标类中，导致实际调用的crossSellOffersConnectBDS根本不是你配置的Mock实例，自然返回默认的null。

修复方式： #

把测试类中的Mock对象类型改成和Adapter类中依赖一致的类型：

@Mock 
private CrossSellOffersConnectBDS crossSellOffersConnectBDS; // 修正为与Adapter中一致的接口/类类型

2. 测试调用的参数顺序错误 #

先看getApplicableOffers的方法定义：

public Offers getApplicableOffers(String channelId, String customerId, String cinSuffix, String countryCode, String interactionPoint, String sessionId, Integer numberOfOffers)

参数顺序是：channelId → customerId → cinSuffix → countryCode → interactionPoint → sessionId → numberOfOffers

但你的测试调用是：

Offers offers = crossSellOffersService.getApplicableOffers("MBSG", "IBOXS007", "00", "SG","NEW_CC_ADDON", "S9718016D", 1);

这里把customerId和sessionId完全搞反了！你Mock的是getBDSCustomerInfo("MBSG", "S9718016D", "00", "SG")，但实际调用时传入的customerId是"IBOXS007"，和Mock的参数不匹配，Mockito自然返回默认的null。

修复方式： #

调整测试调用的参数顺序，严格匹配方法定义：

Offers offers = crossSellOffersService.getApplicableOffers("MBSG", "S9718016D", "00", "SG","NEW_CC_ADDON", "IBOXS007", 1);

3. 额外优化：Mock返回对象与后续参数一致性问题 #

你MockgetBDSCustomerInfo时返回的是sampleBDSResponse()，但后续MockgetCMPOffers时用的是bdsResponse这个Mock对象，这两个不是同一个实例。如果getCMPOffers依赖传入的bdsCustomerHoldings的属性，会导致这个Mock也不生效。

修复方式二选一： #

• 让sampleBDSResponse()直接返回bdsResponse这个Mock对象：

  Mockito.when(crossSellOffersConnectBDS.getBDSCustomerInfo("MBSG", "S9718016D", "00", "SG")).thenReturn(bdsResponse);
  

• 或者用Mockito的匹配器，允许匹配任意BDSCustomerHoldings实例：

  Mockito.when(crossSellOffersConnectCMP.getCMPOffers(any(BDSCustomerHoldings.class), eq("NEW_CC_ADDON"), eq("IBOXS007"), eq(1)))
         .thenReturn(CrossSellOffersConnectCMPAdapterTest.sampleCMPOffer());
  

完整修复后的测试类示例 #

别忘了添加Mock初始化的逻辑（要么用@Before，要么用MockitoJUnitRunner），否则@Mock和@InjectMocks不会生效：

public class CrossSellOffersServiceAdapterTest { 
    @InjectMocks 
    private CrossSellOffersServiceAdapter crossSellOffersService; 
    @Mock 
    private CrossSellOffersConnectBDS crossSellOffersConnectBDS; 
    @Mock 
    private CrossSellOffersConnectCMP crossSellOffersConnectCMP; 
    @Mock 
    private RestTemplate restTemplate; 
    @Mock OffersRequest offersRq; 
    @Mock private BDSRequest bdsRequest ; 
    @Mock private BDSCustomerHoldings bdsResponse; 

    @Before
    public void setUp() {
        MockitoAnnotations.openMocks(this); // 初始化所有Mock对象
    }

    @Test 
    public void getApplicableOffersTest() throws CrossSellOffersException { 
        // Mock BDS调用，返回预设的bdsResponse
        Mockito.when(crossSellOffersConnectBDS.getBDSCustomerInfo("MBSG", "S9718016D", "00", "SG"))
               .thenReturn(bdsResponse); 
        // Mock CMP调用
        Mockito.when(crossSellOffersConnectCMP.getCMPOffers(bdsResponse, "NEW_CC_ADDON", "IBOXS007", 1))
               .thenReturn(CrossSellOffersConnectCMPAdapterTest.sampleCMPOffer()); 
        // 修正参数顺序后的调用
        Offers offers = crossSellOffersService.getApplicableOffers("MBSG", "S9718016D", "00", "SG","NEW_CC_ADDON", "IBOXS007", 1); 
        assertNotNull(offers, "response is not null"); 
    } 
}

内容的提问来源于stack exchange，提问作者durgaPrasad