how best test protected member functions?

[Anonymous]

I often find that I would like to test a class at a finer grain than its public interface.  Currently, I am using preprocessor directives in the class to be tested:

#ifdef TEST
public:
#else
protected:
#endif

I don't want to make the protected interface public just so that my test code runs, but I don't know a good way to use 'friend' to solve this problem and the directives sure make the class code ugly.  Maybe a slick macro, but I would rather not have to touch the class code at all.

Does anyone have any thoughts on this?

Thanks in advance,

Jeremy

[coinoperated]

We use a similar technique but use an alias defined in a standard types header:

#ifdef _DEBUG
# define Testable public  // opened for testing
#else
# define Testable // closed for release
#endif

In the code :
#include "OurStdTypes.h"
class ToTest
{
public:
   // public interface
private:
   // always private
Testable:
  // open for testing only
}

Haven't found a less intrusive mechanism but would love to see one..

[coinoperated]

We use a similar technique but use an alias defined in a standard types header:

#ifdef _DEBUG
# define Testable public  // opened for testing
#else
# define Testable // closed for release
#endif

In the code :
#include "OurStdTypes.h"
class ToTest
{
public:
   // public interface
private:
   // always private
Testable:
  // open for testing only
}

Haven't found a less intrusive mechanism but would love to see one..

[Tom Plunket]

Wow, that's something.  :)

My feeling is that if the tests are meant to be intrusive, make them intrusive.

class MyClass
{
   friend class MyClassTest

// stuff
};

class MyClassTest : public CppUnit::Test { };

AFAIAC, this class isn't meant for testing the interface of the class only.  Sometimes you may wish to test just the interface, but I prefer testing each of the member functions with an intrusive mechanism like friendship.  This has the benefit of also not using any preprocessor ugliness.

[Wolfgang Stoecher]

When posting this question to an XP-forum, one of the answers was like this:
"If you want to test a private method, then your class probably has aspects that can be taken out and separated into a new class."
I take the need for testing a private/protected member as a "code smell". Refactoring always solved this problem for me and also resulted in a nicer structure.

Wolfgang

[Anonymous]

First of all, thanks for the feedback.  Unfortunately, I am still searching...

The 'Testable' alias is similar to, but cleaner than what I have been using.  My only gripe would be the name choice; it suggests that the public interface is not testable.

The friend solution is what I first considered, but I would like to avoid dependencies of system code on testing code.

I very much like the 'code smell' solution, but I'm not sure how to refactor my code as it is already quite reduced.  I have a public 'Step(...)' function that is called each "step" which, in turn, calls a list of protected functions (that may very between steps).  I could make all of the functions public to the client, but this would complicate thier code and I see no good reason to expose the protected interface.

Thanks again for the input.  I will meditate on this :)

Jeremy

[Wolfgang Stoecher]

Hi Jeremy,

from your short description I would guess that you have a state-machine and the states in one class?(or is it: container and iterator?)
Do you know the state-machine-compiler (SMC) project at sourceforge? (smc.sourceforge.net)

Wolfgang

[Christian Furst]

The suggestion from Tom Plunket look nice but how do I accomplish it with CppUnit.

My test class is declare like:
  template<typename T> class TestCMyClass(T t);

I tried something like this:
class CMyClass
{
  #ifdef _TESTCASECODE
    template<typename T> friend class TestCMyClass(T t);
  #endif

[Tom Plunket]

using _TESTCASECODE as an identifier is a violation of the rules of the C++ language.  For more information on this and how to make template classes friends (I don't know how to do that off hand), ask on comp.lang.c++.