Flutter单元测试：Mockito多存根引发MissingStubError问题

问题场景 #

使用Mockito 5.3.2测试BookingService的createBooking方法时，触发MissingStubError，提示调用createCashbookItem(Instance of 'CashbookItem')无匹配存根。该方法逻辑为：当传入的Receipt的paymentType等于kPaymentTypeBar时，会调用CashbookItemRepository的createCashbookItem方法。

原因分析 #

Mockito默认使用严格对象实例相等性匹配存根。测试代码中手动创建了cashbookItem并基于该实例设置存根，但待测试方法createBooking内部是通过CashbookItem.fromReceipt(receipt)生成全新的CashbookItem实例——两个实例内存地址不同，因此Mockito无法匹配到对应的存根。

解决方案 #

方案1：使用参数匹配器（推荐） #

通过Mockito的参数匹配器，忽略实例本身，匹配对象的核心属性。

步骤1：定义自定义匹配器

创建一个匹配器函数，对比CashbookItem的关键属性：

Matcher matchesCashbookItem(CashbookItem expected) {
  return predicate((actual) {
    final item = actual as CashbookItem;
    // 根据业务需求，对比需要验证的核心属性
    return item.amount == expected.amount &&
        item.paymentType == expected.paymentType &&
        item.category == expected.category &&
        item.documentNumber == expected.documentNumber;
  });
}

步骤2：更新存根逻辑

用自定义匹配器替换原有的实例匹配：

when(mockCashbookItemRepository.createCashbookItem(argThat(matchesCashbookItem(cashbookItem))))
    .thenAnswer((_) async => const Right(unit));

如果不需要精确匹配，也可以用any()快速解决（适合简单场景）：

when(mockCashbookItemRepository.createCashbookItem(any()))
    .thenAnswer((_) async => const Right(unit));

方案2：为CashbookItem实现相等性判断 #

重写CashbookItem类的==运算符和hashCode方法，让内容相同的实例被认为相等：

class CashbookItem {
  // 类属性定义
  final double amount;
  final String paymentType;
  final String category;
  final String documentNumber;

  CashbookItem({
    required this.amount,
    required this.paymentType,
    required this.category,
    required this.documentNumber,
    // 其他属性
  });

  // 从Receipt创建的方法
  factory CashbookItem.fromReceipt(Receipt receipt) {
    return CashbookItem(
      amount: receipt.amount,
      paymentType: receipt.paymentType,
      category: receipt.category,
      documentNumber: receipt.documentNumber,
      // 其他属性映射
    );
  }

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is CashbookItem &&
          runtimeType == other.runtimeType &&
          amount == other.amount &&
          paymentType == other.paymentType &&
          category == other.category &&
          documentNumber == other.documentNumber;

  @override
  int get hashCode => Object.hash(amount, paymentType, category, documentNumber);
}

完整测试代码（方案1示例） #

@GenerateMocks([CashbookRepository, ReceiptRepository, CashbookItemRepository])
void main() {
  late BookingService bookingService;
  late MockCashbookRepository mockCashbookRepository;
  late MockCashbookItemRepository mockCashbookItemRepository;
  late MockReceiptRepository mockReceiptRepository;

  setUp(() {
    mockCashbookRepository = MockCashbookRepository();
    mockCashbookItemRepository = MockCashbookItemRepository();
    mockReceiptRepository = MockReceiptRepository();
    bookingService = BookingServiceImpl(
      receiptRepository: mockReceiptRepository,
      cashbookItemRepository: mockCashbookItemRepository,
      cashbookRepository: mockCashbookRepository,
    );
  });

  // 自定义匹配器
  Matcher matchesCashbookItem(CashbookItem expected) {
    return predicate((actual) {
      final item = actual as CashbookItem;
      return item.amount == expected.amount &&
          item.paymentType == expected.paymentType &&
          item.category == expected.category &&
          item.documentNumber == expected.documentNumber;
    });
  }

  group("bookings", () {
    var t_OldReceipt = Receipt.empty();

    test("create booking should call createCashbookItem when paymentType is bar", () async {
      // Arrange
      t_OldReceipt = t_OldReceipt.copyWith(
          amount: 10,
          totalAmount: 10,
          taking: true,
          category: "test",
          taxRate: 0,
          paymentType: kPaymentTypeBar,
          documentNumber: "1",
          taxAmount: 0,
          receiptDate: DateTime.now(),
          year: "2023",
          yearMonth: "20232",
          yearMonthDay: "2023210",
          contact: Contact.empty());

      final cashbookItem = CashbookItem.fromReceipt(t_OldReceipt);

      when(mockReceiptRepository.createReceipt(t_OldReceipt))
          .thenAnswer((_) async => const Right(unit));
      when(mockCashbookItemRepository.createCashbookItem(argThat(matchesCashbookItem(cashbookItem))))
          .thenAnswer((_) async => const Right(unit));

      // Act
      final result = await bookingService.createBooking(t_OldReceipt);

      // Assert
      expect(result, const Right(unit));
      // 验证createCashbookItem是否被调用一次
      verify(mockCashbookItemRepository.createCashbookItem(argThat(matchesCashbookItem(cashbookItem)))).called(1);
      // 验证receiptRepository的createReceipt被调用
      verify(mockReceiptRepository.createReceipt(t_OldReceipt)).called(1);
    });
  });
}

验证方法调用 #

使用Mockito的verify()方法确认createCashbookItem是否被正确调用：

• 精确验证：结合自定义匹配器，确保传入的参数符合预期
• 次数验证：通过.called(n)指定调用次数（n为整数，比如1表示调用一次）

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