[Boost-users] Comments / Advice on using Boost Test Library

From: Dave Steffen (dgsteffen_at_[hidden])
Date: 2006-09-14 20:09:42

Hi Folks,

We've been happy Boost Test Library customers for over a year now,
slowly building up a set of unit tests for a large legacy code base.
There's no question that it's Good Stuff.  Specifically, everything we
do is some variation on a BOOST_AUTO_UNIT_TEST-y sort of thing; the
extremely low amount of "typing overhead" is a big part of why so many
people are writing unit tests (these unit tests are cheap, as unit
tests should be).

What I'd like to ask the Boost community about is this: how to go
about unit testing private class methods.

One answer is "don't; only unit test the public interface", which is
fine as far as it goes.  However, most of our work is extremely
mathematical, so it's not uncommon to see something like

class Base { ... public interface, etc ...};

class Derived : public Base
{
public:

        ... goodies in here ...

private:

        double HelperFn1();
        bool   HelperFn2(int, double, KalmanFilter&);
};

where HelperFn1 and HelperFn2 are extremely non-trivial mathematical
operations.  Yes, exercising the public interface will signal mistakes
in the helper functions, but can't do much to poke at them in depth,
or help pinpoint exactly what chunk of math isn't right.  What we want
is to be able to write unit tests that poke and prod such private
member functions directly.

Another answer is "give your class a friend "tester" class, that uses
its frienship to give the unit tests access to the class' guts".  We've
been doing that for about a year now; not the most elegant, but an
effective solution.  Unfortunately, it doesn't work for the thing I
wrote this afternoon; I'll skip the details.

Another horrible, but effective, possibility is to 

    #define private public
    #include "ClassToTest.h"
    ...

(only in the unit test suites!) and muck about in the class's guts
directly.  This is the only way I know of to get into the rather
complicated template-class-heirarchy-interface-wrapper thing that I
just built.

What kinds of techniques are you all using out there?

Thanks very much for any comments!

----------------------------------------------------------------------
Dave Steffen, Ph.D.      
Software Engineer IV              Disobey this command!
Numerica Corporation
ph [phone] x27    
fax [phone]                   - Douglas Hofstadter
dgsteffen_at_[hidden]