Re: [boost] Is there interest in unit testing both passing and failing BOOST_MPL_ASSERTs?

Subject: Re: [boost] Is there interest in unit testing both passing and failing BOOST_MPL_ASSERTs?
From: Ábel Sinkovics (abel_at_[hidden])
Date: 2011-09-15 15:27:30

Hi,

The suggestions I've made are all based on a library I have already
implemented: this is the metatest (sub)-library of mpllibs I mentioned
on another thread (Template metaprogramming libraries). You can download
and try it out.

The repository is here:
https://github.com/sabel83/mpllibs
The source tree follows the structure of the Boost libraries but uses
the mpllibs namespace (and macro prefix) instead of boost.

Documentation is here:
http://abel.web.elte.hu/mpllibs/metatest/index.html

Examples on how to use it: in the libs/metatest/example directory of the
source tree. You can find a number of the unit tests of Boost.MPL ported
to use metatest in the boost_mpl_unit_test example.

> BOOST_MPL_ASSERT(( mpl::equal<preorder_adj::type, mpl::vector<A,B,C,D,E,F,G,A> > ));

Gordon, you can rewrite this example using metatest:

----
#include <mpllibs/metatest/test.hpp>
const mpllibs::metatest::suite_path suite("example_test_suite");
typedef
  mpl::equal<preorder_adj::type, mpl::vector<A,B,C,D,E,F,G,A> >
  my_test;
MPLLIBS_ADD_TEST(suite, my_test)
----
You need a main function as well. You can use one of the already created
ones (eg. "#include <mpllibs/metatest/main.hpp>"). It will show you a
pretty-printed error message in case of a failure.
The way the library works at the moment: instead of asserting or
throwing exceptions it collects the results and pretty-printed reasons
in a runtime tree structure. A main() function can browse this tree and
display a report or call the assertion solution of any testing tool
(such integration code for Boost.Test is included - see documentation).
The reason I implemented it this way was that I could easily (by
implementing/changing the integration function only) use it in any
testing framework.
I have tested the rest of the mpllibs libraries using this tool, you can
take a look at the tests of those libraries as examples as well.
Ben, your idea of throwing an exception for a failed compile-time
predicate can be easily implemented in this library by using a template
function taking the predicate as template argument.
Note that Boost.MPL data-type support for the pretty-printer (to_stream)
is proof-of-concept only in its current form. That should be implemented
inside Boost.MPL instead (the rest of the libraries in mpllibs implement
pretty-printing support themselves as well).
If you have a chance to play with it, I'm happy to receive feedback and
suggestions.
Regards,
  Abel