Here’s Knuth in an interview:
As to your real question, the idea of immediate compilation and “unit tests” appeals to me only rarely, when I’m feeling my way in a totally unknown environment and need feedback about what works and what doesn’t…
Hmm, people who are “feeling their way in a totally unknown environment”… Like new contributors to an open-source project or a new employee doing maintenance work on a project after the original team has gone on to other companies.
…otherwise, lots of time is wasted on activities that I simply never need to perform or even think about. Nothing needs to be “mocked up.”
Good for him. Here on Planet Earth, developers are often asked to work on projects they didn’t design and implement themselves, and do so in a way that doesn’t horribly break something that already exists. Or work with others because your desired endstate and timeline are not such that you can do it yourself or work things piecemeal and take it back for a redesign. </snark>