It is considered good practice to develop and maintain the test suite with high level of test coverage, i.e., the tests that execute every single statement, every line of the code and then validate the result.
The GNU’s gcov is a tool that analyses the frequency of execution of each line of the code. For more details see GNU documentation http://gcc.gnu.org/onlinedocs/gcc/Gcov.html
To invoke gcov on krb5 tree, do configure with the following options and run the tests:
./configure CFLAGS="-fprofile-arcs -ftest-coverage -O0" LIBS=-lgcov make make check
It will result into creation of the new helper files with the extentions gcno and gcda.
To validate the test coverage of the specific file, change the directory to its location and run
gcov -o filename.so.gcno filename.c
To see the test coverage of the filename.c open a newly created file filename.c.gcov in the editor.
Some recent test coverage result can be found at the http://k5wiki.kerberos.org/wiki/Test_coverage