By the way: Clozure CL has a code coverage tool that is (I think) easy to
use and that produces an easy to understand color-coded html file as output.
(http://trac.clozure.com/ccl/wiki/CodeCoverage)
Recently, I used the tool to find untested branches in a new version
of orthopoly--it helped me find some bugs and it encouraged me to append
a few dozen tests.
I have not tried to build Maxima using the code coverage tool. That might
be fun for somebody to try.
Of course, I assume that other compilers have such tools too.
Barton