[mseebach]

In theory. In practice, the code will often have corner case behaviours that eludes any of the tests, yet are still important.

As an aside, as I understand it, refactoring was popularised as a response basically to this conundrum - it's a technique for reorganising code without changing its functionality. So you can gradually "rewrite" your two page function without losing the accumulated knowledge.

[3pt14159]

Unless we really stretch the word "refactor", my "in practice" is different than yours. I've done plenty of re-writes that fixed more unknown bugs than re-opened previously solved ones.