Re: [Boost-users] [Unit-Test] How to test private functions

3 May 2006

      Ed Johnson wrote:
...
Paul Giaccone wrote:
...
Ryo IGARASHI wrote:
...
On 3/23/06, Leif Gruenwoldt  wrote:
...
Is there a way to test the private functions of a class without moving
them into public scope during test?
What are some strategies for this?
Try following evil hack.
// someclass_test.hpp
#define private public
#define protected public
#include 
#undef protected
#undef private
Evil, evil, evil!
Slightly less so is what I have done in my code. Define a variable (say, 
TESTING) in the makefile or preprocessor definitions of your test 
program. In your class definitin, change "private:" to the following:
#ifdef TESTING
public:
#else
private:
#endif
Of course, you leave TESTING undefined (or make sure it is undefined) in 
your non-test program.
It's perhaps not nice to look at, but it's less nasty than the above 
hack, IMO.
Paul
Hi Paul,
I wanted to add to your post. I am trying to figure out a good 
solution to Leif's problem for my own project.  Your solution seemed 
good, but I also want the ability to test just the public interface, 
without simultaneous access to the private data.  When I use the #ifdef 
TESTING solution, my unit tests never test the classes as they will be 
used by an end user because all class data is always public. This could 
lead to a false sense of security from my unit tests.
I'm not sure why you say the class data is public. The #ifdef I was 
proposing is for member functions only, so the class data remains private.

That said, I've now moved to a less hacky approach, which is to define 
member functions used by the test programs only that call the private 
member functions. For example:

private:
    int foo(int a);

#ifdef TESTING
public:
    int foo_test(int a)
    {
       return foo(a);
    }
#endif

I'm not sure if this is a preferable alternative to your idea of 
separating members into their own test suites, but it certainly seems 
simpler.

Paul