Tiny Tips : Testing protected method without using friendship in C++

Assume you have this class to test:

MyClass.h

class MyClass {
public:
    float publicMethod();
protected:
    float criticalInternalMethod();
};

criticalInternalMethod() implement a complex business logic or algorithm, but it is too internal to make it part of public API. How to test it ?

With GoogleTest, you can use the FRIEND_TEST macro. But it requires putting google header in public API, and a macro in class definition.

What you can do instead is this:

MyClassTest.cpp

class MyClassTest : public MyClass
{
public:
    using MyClass::criticalInternalMethod;
};

TEST(MyClassShould, computeGoodResult)
{
    MyClassTest myClass;
    EXPECT_EQ(myClass.criticalInternalMethod(), 12);
}

This doesn't work for private method, but at least it avoids polluting public header only for the sake of testing.