为何调用Helper方法的JUnit测试未按预期抛出异常？

相关代码 #

Service类 #

public class AccountServiceImpl {
    @Autowired
    AccountHelper accountHelper;

    @Override
    public Account createAccount(Account account) throws CustomerNotFoundException {
        accountHelper.checkAccountTypeForCustomer(account);
        return accountRepository.save(account);
    }
}

Helper类 #

public void checkAccountTypeForCustomer(Account acc) throws CustomerNotFoundException {
    Boolean customerExists = customerRepository.existsById(acc.getCustomerId());
    if(!customerExists) {
        throw new CustomerNotFoundException("604", Message.CUSTOMER_NOT_FOUND);
    }   
}

测试类 #

@ExtendWith(MockitoExtension.class)
public class AccountServiceTest {

    @Mock
    private AccountRepository accountRepository;

    @Mock
    private CustomerRepository customerRepository;

    @Mock
    private AccountHelper accountHelper;

    @InjectMocks 
    private AccountService testService;

    @Test
    void testCreateAccount() throws CustomerNotFoundException {
        Account account = Account.builder()
                .accountType(AccountType.SAVINGS)
                .openingBalance(BigDecimal.valueOf(3000))
                .ifsc("IFSC1")
                .customerId(1)
                .build();
        testService.createAccount(account);
    }
}

问题原因 #

你当前测试未抛出异常的核心问题是：你把AccountHelper声明成了@Mock对象。Mockito的Mock对象默认不会执行原类的真实方法逻辑，调用Mock对象的方法时只会做“空操作”——既不会执行检查客户是否存在的逻辑，也不会抛出异常，所以测试能顺利通过。

而当你把checkAccountTypeForCustomer()的逻辑移到Service方法内部时，这段逻辑属于Service的真实代码（没有被Mock），此时执行测试时会真实检查客户是否存在，自然会抛出异常导致测试失败，这符合预期。

修正方案 #

方案1：测试AccountHelper的真实逻辑 #

如果要验证AccountHelper的真实检查逻辑是否生效，不要把它声明为@Mock，改用@Spy（保留真实方法逻辑，同时可对其依赖的Mock对象进行配置）：

@ExtendWith(MockitoExtension.class)
public class AccountServiceTest {

    @Mock
    private AccountRepository accountRepository;

    @Mock
    private CustomerRepository customerRepository;

    @Spy // 改用@Spy，保留AccountHelper的真实逻辑
    private AccountHelper accountHelper;

    @InjectMocks 
    private AccountService testService;

    @Test
    void testCreateAccount_ThrowsCustomerNotFound() {
        Account account = Account.builder()
                .accountType(AccountType.SAVINGS)
                .openingBalance(BigDecimal.valueOf(3000))
                .ifsc("IFSC1")
                .customerId(1)
                .build();
        
        // 模拟客户不存在的场景
        when(customerRepository.existsById(1)).thenReturn(false);
        
        // 断言调用createAccount时会抛出异常
        assertThrows(CustomerNotFoundException.class, () -> testService.createAccount(account));
    }
}

方案2：验证Service对AccountHelper的调用逻辑 #

如果只是要验证Service层是否正确调用了AccountHelper的方法，同时模拟异常场景，可以保留@Mock的AccountHelper，手动指定其方法行为：

@ExtendWith(MockitoExtension.class)
public class AccountServiceTest {

    @Mock
    private AccountRepository accountRepository;

    @Mock
    private CustomerRepository customerRepository;

    @Mock
    private AccountHelper accountHelper;

    @InjectMocks 
    private AccountService testService;

    @Test
    void testCreateAccount_ThrowsCustomerNotFound() {
        Account account = Account.builder()
                .accountType(AccountType.SAVINGS)
                .openingBalance(BigDecimal.valueOf(3000))
                .ifsc("IFSC1")
                .customerId(1)
                .build();
        
        // 模拟调用checkAccountTypeForCustomer时抛出异常
        doThrow(new CustomerNotFoundException("604", Message.CUSTOMER_NOT_FOUND))
            .when(accountHelper).checkAccountTypeForCustomer(account);
        
        // 断言会抛出异常
        assertThrows(CustomerNotFoundException.class, () -> testService.createAccount(account));
        
        // 验证AccountHelper的方法确实被Service调用
        verify(accountHelper).checkAccountTypeForCustomer(account);
    }
}

理解误区总结 #

你混淆了Mockito中Mock对象的作用：Mock对象是用来模拟依赖组件的行为，默认不会执行原类的真实方法逻辑。你原本以为Mock的AccountHelper会执行检查客户的逻辑，但实际上它只是一个“空壳”，不会触发任何真实逻辑，自然不会抛出异常。

内容的提问来源于stack exchange，提问作者Pavithra