Given the following code example which represents a simplification of a much larger project:

class IEaterOfCake
{
    public:
        virtual void EatCake() = 0;
};

class CakeMaker
{
    public:
        CakeMaker(IEaterOfCake & e) : mCakeEater(e) {}
        void MakeCake() { mCakeEater.EatCake(); }
    protected:
        IEaterOfCake & mCakeEater;
};

class HungryMan : public IEaterOfCake
{
    public:
        HungryMan() : mCakeMaker(*this) {}
        void HaveLunch() { mCakeMaker.MakeCake(); }
        virtual void EatCake() override {/* mmmm cake */};
    private:
        CakeMaker mCakeMaker;
};

int main()
{
    HungryMan m;
    m.HaveLunch();
}

I can nicely unit test CakeMaker with a test like:

TEST(sometest)
{
    class TestEater : public IEaterOfCake
    {
        virtual void EatCake() override {/* test cake is yummy */};
    } t;
    CakeMaker cm(t);
    cm.MakeCake();
}

Now, I would like to test HungryMan with a mock CakeMaker. It is too complex to try test HunrgyMan and CakeMaker as a single unit. In practice HungryMan has several internal classes feeding into it in a similar way. The number of possibilities goes up exponentially!

Dependency injection of a CakeMaker (or interface to) would be ideal, but the hope was to hide them inside the HungryMan class. And I am not sure how to make sure references to teh dependencies would be initialised at construction, as those dependencies also need to reference the Hungry man . Note that ‘new’ cannot be used in this project, dynamic allocation is not allowed.

I am after suggestions on how to better structure this project so that HungyMan can be unit tested with a mock/test implementation. Currently I conditionally compile in a different type for mCakeMaker (MockCakeMaker). But I still have the issue where mCakeMaker is private and inaccessible to manipulate for testing.

I hope I explained OK, I struggled a bit!