There are tons of blogs and articles trying to find an answer on
How to measure software quality. As this is a rather
difficult question and we don't really have a good tool for
measuring it Michael Schwern - one of the key persons in the
Perl QA team - came up with the idea to measure
He even created a tool called CPANTS
that measures Kwalitee. The tool is now maintained by Thomas Klausner
with my occasional additions to the code.
CPANTS has currently 48 metrics. Some are direct such as has_test
others are indirect such as is_prereq or some of the recent ones
such as distributed_by_debian.
is_prereq indicates if the module is used by some other
module of some other author on CPAN. Using this as a quality indicator
uses the same argument as in the academics, where the important metric
is not how many articles have you written but rather how many other
articles references yours and how important those articles are.
Google uses the same idea in ranking pages.
I assume the same is true on CPAN. CPAN authors are usually picky.
So if a CPAN author uses module X that probably means modules X
is good. Or at least unavoidable.
In a similar way we have added a set of new metrics:
- distributed_by_debian indicates if the module has
been included in Debian.
Inclusion in a Linux distribution likely means there is
a need for that module in the user base. In return that
probably means the module is, well, usable.
(Currently there are only 790 modules listed as such due to
some fragmentation in the way Debian maintains Perl modules
but I hope this will be soon resolved.)
- latest_version_distributed_by_debian indicates if the
version included in Debian is the latest from CPAN.
Obviously this indicator has some problems.
A module that has frequent updates will fail this
metric most of the time as the Debian people take their
time upgrading the module. After all they want to make sure
that they only include good versions of a module. So take this
metric with appropriate caution.
Debian has its own bug reporting system, separate from
RT used by CPAN authors.
It is quite possible that there is a bug in the
version distributed by Debian that has already been fixed on
CPAN but on the long run, modules without open bug reports are
likely to be of better quality for some meaning of quality.
- has_no_patches_in_debian As the Debian maintainer see themselves
responsible for providing high quality software to their users
sometimes they fix bugs in the software they distribute. These fixes
are called patches. Normally these patches should be integrated back
to the main version of the module on CPAN and then the Debian maintainer
should be able to update the version they distribute by a unpatched
Still as long as there are patches for a module it means there is a bug
somewhere in the module on CPAN.
In addition there is a new experimental metric called
Most of the CPAN modules come with plenty of tests.
The CPAN Testers
report any test failure which is really cool.
Still sometime I encounter modules that while they pass their test suit
they also generate warnings during the test execution.
These warnings are probably never reported as most people
run the tests in an unattended mode.
For now it seems that the best way to catch and report these warnings
is by using Test::NoWarnings in every test script. So this new
metric checks if all the test script use it.
The metrics concerting Debian server two purposes. On one hand
they can be used as indicators for the kwalitee of a module.
On the other hand providing an easy way for CPAN authors to
monitor what happens to their module can help resolving
issues encountered in Debian.
We started with Debian but I really hope soon we'll be able to hook up
other distributions too such as FreeBSD
James E Keenan
related on module-authors list
related on perl-qa list
Published on 2008-06-07 by Gabor Szabo