covsrv

This is a small tool that helps increase test coverage. Some procedures like malloc() generally fail very rarely, meaning that error recovery paths tend to be undertested. The solution that I came up with was to have a server keep track of which lines of code have been executed, and inform a test program that a certain call should fail to test out a new error recovery path.

covsrv provides a macro, covsrv_die(), that returns 1 if a line is run for the first time during a test run, and 0 otherwise. The idea is that any/all functions that can fail should be wrapped in a macro that checks covsrv_die(). Something like the following for malloc():

/* replace calls to malloc() with mallocc() to make them fail during testing */
#define mallocc(n) ({covsrv_die() ? NULL : malloc(n)})

./scripts/coverage (in cooperation with the Makefile) shows an example of what roughly needs to be done to set up coverage testing for a project with gcc and lcov. Open coverage/index.html with your web browser of choice, and you should see that all lines in tests/pass.c are exercised. tests/fail.c contains a fairly common but dangerous pattern of realloc(), which practically always succeeds, but fails during our test run.

Future work

It would probably be useful to add functionality to always fail some specific call to make it easier to debug the error recovery path from gdb.

Example integrations into projects that use autotools or cmake would probably be useful.