I just built a large web app over the last 6 months and ignored unit tests (as in, there aren’t any). 

This week, I’m going to add tests. ✅

This is the correct way.
Unless you’re creating a library or framework, test manually until the product stabilizes. Then add tests to enforce stability. Too many tests too soon creates instability

Better later than never

I actually don’t think TDD is a good approach in new projects as code tends to change and tests break often

Goodluck man. Would definitely not be super fun lol