How to test a protected member from multiple inheritance in GoogleTest?

Question

Imagine I have a Foo class which contains a protected member. Foo is my template base class. Then I have a Bar class, which inherits from Foo. The protected member will be private within Bar.

I need to make a test which I need to access the protected member from my Foo base class as seen below.

#include <gtest/gtest.h>

template <typename T>
class Foo
{
public:
    int set() { mMember=1; }    
protected:
    int mMember;
};

class Bar : public Foo<int>
{};


namespace
{
    class myTestUT : public Foo<Bar>, public testing::Test { };

    TEST_F(myTestUT, how_can_i_test_this){
        Bar bar;
        bar.set(); // ALL GOOD, set() is public!

        ASSERT_EQ(bar.mMember, 1); // ERROR! mMember is protected! Why can't I access it since I am inheriting it?
    }
}

On my test setup I have class myTestUT : public Foo<Bar> which will be a bridge to have access to the Foo members (public and protected), so why can't I access my mMember method?

Please note that I know that mMember could be set on the constructor of Foo, but that is not the question here as I created this small snippet to illustrate my problem.

I saw this question, but this doesn't contain my problem with multiple-inheritance.

Answer 1

why can't I access my mMember method?

It is not my mMember, it is bar's member.

GoogleTest manual:

When you need to test the private or protected members of a class, use the FRIEND_TEST macro to declare your tests as friends of the class.

template <typename T>
class Foo
{
public:
    void set() { mMember=1; }    
protected:
    int mMember;
    FRIEND_TEST(myTestUT, how_can_i_test_this);
};

class Bar : public Foo<int>
{};

class myTestUT : public Foo<Bar>, public testing::Test { };

TEST_F(myTestUT, how_can_i_test_this){
    Bar bar;
    bar.set();

    ASSERT_EQ(bar.mMember, 1);
}

You have to remove the unnamed namespace, or use a named namespace. https://godbolt.org/z/3h8q96Ecj