if I have a class with a helper (private member) class within it, like this
class Obj;
class Helper {
friend class Obj;
private:
int m_count;
Helper(){ m_count = 0;}; // Note this is a private constructor
void incrementCount(){
++m_count;
};
};
class Obj {
Helper *m_pHelper;
// note that this is a private getter
int getHelperCount() { return m_pHelper->m_count; };
// the public API starts here
public:
Obj() { m_pHelper = new Helper(); };
void incrementCount(){ m_pHelper->incrementCount(); };
};
So how may I TDD such a system?
auto obj = new Obj();
obj->incrementCount();
// what to assert???
That is my question and the following is just some background.
If noone outside the class should be interested, then your tests should not be interested either. – Arne Mertz
If nobody is interested in the value outside the class, why are you – utnapistim
Even if no one outside needs the value, I may still want to know that if it's set correctly, as it is used by other self contained internal method of the class that use that value. Maybe the value is the speed where the controller will use it to update the model. Or maybe it's the position where the view will use it to draw something on the screen. And in fact all other components of Obj would be able to access that variable. It may be a bad design issue, and in this case I would like to know what better alternatives I can have. The design is listed in the background section at the bottom of this post.
define private public - Marson Mao
Love this ingenious abuse of keywords haha. But may not be concluded as the best solution just yet.
You need to "expose" the friendship relation in the header of your class. Thus you have to acknowledge there the existence of a class used to test yours. If you use the pImpl idiom, you could make the members of the pImpl itself all public, the pImpl itself private and give your unit tests access to the pImpl - CashCow
Does this mean that I should friend the test in my original class? Or add extra "test" methods to it? I just started TDD very recently. Is it common (or better is it good) to intrude the original class with test class dependency? I don't think I have the appropriate knowledge to judge. Any advice on this?
Miscellaneous: AFAIK TDD is not just writing test, but instead a development process. I have read that I should only write tests to the public interface. But the problem is, like the situation in question, most of the codes etc are contained within private class. How may I use TDD to create these codes?
FYI if you would like to know why I am making a private class: I am developing a game from cocos2dx. The game engine adopts a Node tree structure for the updates, rendering etc and every game object would inherit from a Node class provided in the engine. Now I want to implement the MVC pattern on a game object. So for each object I basically created a Object class with 3 helper classes corresponding to each of the MVC components named ObjectModel, ObjectView, ObjectController. Theoretically no one should access the MVC classes directly and would only be accessed somehow through the Object class so I make the 3 of them private. The reason of making the MVC components explicitly as classes is because the View and Controller are updating at different rates (more specifically the Controller performs frame dependent updates, while the View do a simple interpolation based on the model data). The Model class is created purely for religious reasons lol.
Thanks in advance.
The #define private public trick can have side effects with the way some compiler are mangling function symbols (Visual c++ compiler is including access specifier in its name mangling)
You can also change visibility with the using statement :
struct ObjTest : public Obj
{
using Obj::incrementCount;
}
But like other people said, try to not test private stuff if possible.