How about "buckshot testing"? I wrote a file system test that made every single API call with null arguments, good arguments, illegal arguments and then logged the error code. We ran this against every release of the OS and simply dif'd the result against the previous release run. It not only aided in bugfinding, it identified necessary release notes about API differences. The bigger point is, you have a computer at your disposal. It can make LOTS of calls in a short time. Try calling that function with every conceivable argument. Once you have a baseline, a diff tool can reveal everything.