I remember reading about a study about a very different style of development from years ago, where automated testing was NEVER done, but instead formalized models of the program were created and mathematically verified.
If I remember correctly, the final result was a similar level of quality to an extensively tested system developed today, and the code tended to be of somewhat higher quality thanks to the extra thought put into it. (But I'm only going off vague memories here... I might be misremembering)