如何让GMock对象返回固定std::forward_list？编译报错求助

我编写了如下单元测试代码：

TEST(AccountServiceShould, print_a_statement_containing_all_transactions) {
    auto transactionRepository = new TransactionRepositoryMock;
    std::forward_list<model::Transaction *> transactionList;
    auto statementPrinter = new StatementPrinterMock;

    transactionList.assign({transaction("22/12/2019", 1000)});

    ON_CALL(
            *transactionRepository,
            all()
    )
            .WillByDefault(Return(transactionList));

    Clock *myClock = new Clock;

    auto accountService = new AccountService(transactionRepository, myClock);

    EXPECT_CALL(*statementPrinter, print(Eq(transactionList)));

    accountService->printStatement();

    delete accountService;
    delete transactionRepository;
    delete myClock;
    delete statementPrinter;
}

编译时出现如下错误：

No viable conversion from 'internal::ReturnAction<forward_list<Transaction *, allocator<Transaction *>>>' to 'const Action<std::forward_list<model::Transaction, std::allocator<model::Transaction>> ()>' 
candidate template ignored: requirement 'internal::disjunction<std::is_constructible<std::function<std::forward_list<model::Transaction, std::allocator<model::Transaction>> ()>, testing::internal::ReturnAction<std::forward_list<model::T... 
candidate template ignored: could not match 'Action' against 'ReturnAction' 
explicit constructor is not a candidate 
candidate template ignored: could not match 'OnceAction' against 'Action' 
candidate template ignored: requirement 'conjunction<testing::internal::negation<std::is_same<void, std::forward_list<model::Transaction, std::allocator<model::Transaction>>>>, testing::internal::negation<std::is_reference<std::forward_... 
passing argument to parameter 'action' here

尝试修改transactionList类型、使用动态对象甚至自定义MATCHER_P都无法解决，求帮助！

错误原因分析 #

核心问题是类型不匹配：

• 你的TransactionRepositoryMock::all()方法的返回类型被定义为std::forward_list<model::Transaction>（对象列表）
• 但你实际传入的transactionList是std::forward_list<model::Transaction*>（指针列表）
  Google Mock无法在这两种不兼容的类型之间完成转换，因此抛出编译错误。

解决方案 #

1. 对齐mock方法与变量的类型

先确认TransactionRepositoryMock中all()的签名，根据不同的定义调整代码：

• 如果mock定义为返回对象列表：

  class TransactionRepositoryMock : public TransactionRepository {
  public:
      MOCK_METHOD(std::forward_list<model::Transaction>, all, (), (override));
  };
  

  则修改transactionList类型为对象列表：

  std::forward_list<model::Transaction> transactionList;
  transactionList.assign({model::Transaction("22/12/2019", 1000)});
  

• 如果mock定义为返回指针列表：

  class TransactionRepositoryMock : public TransactionRepository {
  public:
      MOCK_METHOD(std::forward_list<model::Transaction*>, all, (), (override));
  };
  

  则确保transactionList的元素为有效指针（注意后续清理避免内存泄漏）：

  std::forward_list<model::Transaction*> transactionList;
  transactionList.assign({new model::Transaction("22/12/2019", 1000)});
  

2. 修正EXPECT_CALL的参数类型

确保EXPECT_CALL中print方法的参数类型，与StatementPrinterMock::print的定义、transactionList类型完全一致。

3. 优化内存管理（可选）

避免手动delete导致的内存泄漏或错误，建议使用智能指针：

TEST(AccountServiceShould, print_a_statement_containing_all_transactions) {
    auto transactionRepository = std::make_unique<TransactionRepositoryMock>();
    std::forward_list<model::Transaction> transactionList;
    auto statementPrinter = std::make_unique<StatementPrinterMock>();

    transactionList.assign({model::Transaction("22/12/2019", 1000)});

    ON_CALL(*transactionRepository, all())
        .WillByDefault(Return(transactionList));

    auto myClock = std::make_unique<Clock>();
    auto accountService = std::make_unique<AccountService>(transactionRepository.get(), myClock.get());

    EXPECT_CALL(*statementPrinter, print(Eq(transactionList)));

    accountService->printStatement();
}

内容的提问来源于stack exchange，提问作者Muc