Quoth TFA: "So while we gain quality from the bugs fixed, we lose quality when adding all the new features. For some programs where the functionality is fixed,

Quoth TFA: "So while we gain quality from the bugs fixed, we lose quality when adding all the new features. For some programs where the functionality is fixed, for example unix commands like cat, grep or ls, I imagine they have become very stable, because eventually all of the bugs have been found and fixed." For me, this is the greatest insight that is glossed over. The Unix Philosophy of reducing a program into a system of small composable parts which have a specific and FIXED functionality does more to reduce bugs and stop program rot (via unending features) than reams of tests on a constantly shifting codebase. The problem with monolisthic codebases, even with a test framework, is that you still cant guarantee that one change in one part wont adversely affect another part. Process isolation at least limits bugs to "passing the wrong message".