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Subject: Re: [std-proposals] Friend namespace
From: chibane nadir (organicoman_at_[hidden])
Date: 2020-12-06 14:19:39


 @Peter: usually it is true to avoid testing private members, but for the sake of preventing a subsequent refactor of public API from creating side effects on private members, we need to create test cases with the purpose of fixing invariant in our classes. Also if you look at it in different manner, private members are part of the logic of the classes, which means not testing them could create logic bugs (what i call smart bugs) and refactoring them into public member would expose a lot of the guts of the implementation.
I used to test private members by checking their effects on public members (transitive side effects), but i run into a lot of cases where you cannot pin point the effect of a private member if the public member depends on many of them.
@Arthur O'Dwyer : '  Namespaces, unlike classes, are open.' very true, it would be a great idea if a friended namespace will be like an anonymous namespace, i.e. static to the translation unit it was defined in. expl:
friend namespace XYZ {}; // the friend keyword changes this namespace into a "static" namespace if we can say that!
class toBeTested{    using namespace XYZ;
}
@Ville Voutilainen :  adding an #ifdef preprocessor condition, adds to the maintainability of the class, and convey the meaning that testabilty is optional tho test development is almost mandatory in software building.

My motivation about this proposal is to:- unrestrict the way we test our classes,
- keep implementation details hidden if they should be hidden,
- avoid dogmas of "how to use" or "not to use".- unleash creativity (I'm pretty sure someone will find an interesting way to use this feature other than its intended use)
- and for projects which didn't implement testing from the beginning, they just have to create a friend namespace with functions that shadows the class API, and test the members of that friend namespace, one API at a time.

please advise.
Nadir
   Le dimanche 6 décembre 2020 à 10:24:46 UTC+1, Peter C++ via Std-Proposals <std-proposals_at_[hidden]> a écrit :
 
 To start with, you should not test private stuff. It is private, so it might change. Binding tests to the private parts makes them harder to change, because of the tests, that should make software easier to refactor and change. 
Peter(Test infected since 1997)

sent from a mobile device so please excuse strange words due to autocorrection. Peter Sommerladpeter.cpp_at_[hidden]+41-79-432 23 32

On 6 Dec 2020, at 02:57, chibane nadir via Std-Proposals <std-proposals_at_[hidden]> wrote:

Hello Team,for the purpose of TDD, there is a problem with testing private data members and member functions. some call it black box testing and others do the nasty "#define private public" just to shortcut the visibility of private and protected members to test the classes.I suggest to add the feature of "friend namespace" like the following:
namespace XYZ{    // define here your functions and classes    void test_object_private_data_member_D(object* self,...);
}
class object{    // private data members, and member functions    'sometype' D;
    // public data members, and member functions
// for the purpose of testing this class let's include the members of namespace XYZ as friends so we can access private and protected// members of the current classprivate:
    using friend namespace XYZ; // <---- (A)
};
(A): at this point all the functions and classes defined in the namespace XYZ above will be inserted in the class "object" as friend functions and classes, likewise we will write test cases based on these friend functions and classes since they have access to all"object" class no matter what is their visibility (private, protected or public), and avoiding the need to use the nasty macro hack'#define private public'

i can show a sample of how i use friend functions to create test cases, for interested people.

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