guest@xkcd:/$ vi
You should really use emacs.

guest@xkcd:/$ emacs
You should really use vim.

guest@xkcd:/$ find
What do you want to find? Kitten would be nice.
guest@xkcd:/$ find kitten

{game about a robot finding a kitten, rogue-style}

hahaha

guest@xkcd:/$ cat
You're a kitty!

I don't think you understand the problem the parent described. Unit tests can't help you to diagnose multi-threaded and time-related issues. When you have a bug which only reproduces in the wild once every 3 months, just saying "unit tests" won't allow you to reproduce the bug, fix it and add the test to reproduce this bug to regression. At best you need to create the tools to reproduce the bug yourself, and with certain systems and certain bugs, this can be far from trivial to develop. Multi-threaded and real-time systems are a whole different kettle of fish than basic class design and testing.

You both also forgot Alan Turing.