如何模拟依赖项的成员变量? [英] How to mock a member variable of dependency?

问题描述

我有一个班级和成员:

class A
{
    B obj;
public:
    int f(int i){return obj.g(i);}
}

此处 B obj 是一个依赖项，需要从文件中运行时创建.在类A的单元测试中，我希望使用类型为 int(int)的函数 g 来模拟 B obj .

Here B obj is a dependency that requires run-time creation from a file. In my unit test for class A, I wish to mock B obj, with a function g typed int(int).

如何编写测试代码以模拟 B obj ，然后测试 A :: f .

How can I write my test code, to mock B obj, and then test A::f.

非常感谢.

推荐答案

您需要使用依赖注入来实现此目的.为此，让类 B 从接口继承，并让类 A 持有指向该接口的指针:

You need to use dependency injection to achieve this. To this end, have class B inherit from an interface, and have class A hold a pointer to that interface:

class IB
{
public:
    virtual void g(int i) = 0;
};

class B : public IB
{
public:
    void g(int i) {
        // this is your real implementation
    }
};

此外，要在类 A 中启用依赖项注入，请添加适当的构造函数或setter方法:

Also, to enable dependency injection in class A, add appropriate constructor or setter method:

class A
{
private:
    IB *obj;
public:
    A() : obj(nullptr) {}
    // You don't need both the constructor and setter, one is enough
    A(IB *pB) : obj(pB) {}
    // void setB(IB *pB) { obj = pB; }
    int f(int i) { return obj->g(i); }
};

现在，在生产代码中，您将创建一个 B 类的对象，并将其传递给 A 类的对象(假设我们正在使用构造函数进行注入):

Now, in your production code you create an object of class B and pass it to class A object (assuming that we are using the constructor for injection):

B b;
A a(&b);

在测试阶段，您创建一个模拟类 BMock 并将该类的对象传递给类 A 对象:

During testing phase, you create a mock class BMock and pass an object of that class to class A object:

class BMock : public IB
{
public:
    MOCK_METHOD1(g, int(int));
};

TEST(ATests, TestCase1)
{
    BMock bmock;
    A a(&bmock);

    // Now you can set expectations on mock object, for example that g will
    // return 100 when it receives 50 as argument
    EXPECT_CALL(bmock, g(50)).WillOnce(Return(100));

    // Now act by calling A::f, which will in turn call g from mock object, 
    // and assert on function return value

    ASSERT_EQ(a.f(50), 100);
}

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