Hi,
Juho Snellman recently[1] posted a very useful SBCL-specific coverage tool. http://common-lisp.net/~loliveira/tmp/cffi-tests-coverage/ The results seem pretty good to me: 80.5% code coverage.
This is inded an excellent result given that presumably no tool was ever used before as a guide to achieve a good coverage, i.e. tests were written on an ad-hoc basis. Jumping from 0 to 80 at the first attempt is excellent.
You don't say what these percentages express, so it's pointless to compare that number to other numbers reported in the software reliability community.
Congratulations, Jörg Höhle.