We used strict and warnings. We did module-level testing and ran several hours of simulated missions in the laboratory before delivery, and during integration at the missile range the software ran through several simulated flights while fully integrated with the host flight stack.

It was a few hundred lines of not very dense Perl, mostly doing IPC and spawning compiled commands (that did the heavy lifting for individual control functions) under Gentoo Linux. We used it to control three computers that were connected by an on-bird LAN.