I'm not a huge TDD person, but do appreciate the value of tests around software. This may be a dumb question, but are there any testing tools for Excel? I don't think people would write tests before adding/modifying data and such, but... are there any testing tools that allow you to ensure that your macros and data do what you're expecting, even after changes?
I do not by any means write enough tests for my code, but I have some projects where I've got tests around parts of code, and occasionally I catch regressions when I make changes because of a run of the tests (if I had more tests I'd probably catch more over time).
I've never seen anyone writing custom functionality in Excel that even understood the idea of tests or test/sample data. That is probably a bigger issue with Excel - it encourages people to just throw stuff together and 'start hacking' - with live data, often the only copy of said data - and not understand the potential consequences. Of course, you've usually got a backup of yesterday's data because it's sitting in your inbox, because often Excel files are just emailed around to people, which perhaps encourages yet another sense of 'security' around the process.