I think the real question for me is, suppose you come into maintainership of a legacy application with 100k lines of untested code, where do you start? I think the classical TDD view is "every new change, you add a test for, and so test coverage grows over time."
And that's fine, but I think it's much more valuable before making any functional changes at all, to impose some high level smoke tests that run the entire thing, and do a handful of common, end to end user flows.
And that's fine, but I think it's much more valuable before making any functional changes at all, to impose some high level smoke tests that run the entire thing, and do a handful of common, end to end user flows.