Question

我有一个返回抽象类对象的函数。

AbstractClass some_function(int argument);

我假设如果argument == 1那么some_function应该返回DerivedClassOne的对象，如果argument == 2则应该DerivedClassTwo。{{1}}我想通过简单的单元测试来检查这些假设。

什么是最好的（简单，可读，可靠且独立于任何第三方库和工具）检查方式？

Answer 1

在您的示例中，some_function()按值返回AbstractClass ，这意味着返回的对象会被切片，并且本身只会是AbstractClass 。多态性仅适用于指针和引用。无论哪种方式，您都可以使用dynamic_cast进行验证检查。

例如：

AbstractClass* some_function(int argument);

...

AbstractClass *obj;

obj = some_function(1);
if (dynamic_cast<DerivedClassOne*>(obj) != NULL)
    // returned the correct type...
else
    // returned the wrong type...

obj = some_function(2);
if (dynamic_cast<DerivedClassTwo*>(obj) != NULL)
    // returned the correct type...
else
    // returned the wrong type...

或者：

AbstractClass& some_function(int argument);

...

try {
    dynamic_cast<DerivedClassOne&>(some_function(1));
    // returned the correct type...
}
catch (const std::bad_cast&) {
    // returned the wrong type...
}

try {
    dynamic_cast<DerivedClassTwo&>(some_function(2));
    // returned the correct type...
}
catch (const std::bad_cast&) {
    // returned the wrong type...
}

Answer 2

使用dynamic_cast，如果对象不是预期的子类，则会产生NULL指针。来自维基百科：

int main()
{
    Base* basePointer = new Derived();
    Derived* derivedPointer = NULL;

    // To find whether basePointer is pointing to Derived type of object
    derivedPointer = dynamic_cast<Derived*>(basePointer);

    if (derivedPointer != NULL)
    {
        std::cout << "basePointer is pointing to a Derived class object"; // Identified
    }
    else
    {
        std::cout << "basePointer is NOT pointing to a Derived class object";
    }

    // Requires virtual destructor 
    delete basePointer;
    basePointer = NULL;

    return 0;
}

检查返回的对象是否是C ++单元测试中的预期子类

2 个答案: