Speaking of text editors and tools like that, you can often avoid having tests (or postpone adding them for a long time), if the logic is on the main execution path, meaning you'll execute it every time you run the program, and whatever failures that can happen, are reasonably easy to pinpoint (i.e. the program shows error backtraces or somehow traces problems otherwise).

This is from my experience hacking on Emacs, naturally.

At the same time, projects that you might ship for an employer or a client, are more critical to check for correctness before deploying, and are often more complex to run and check manually on the regular than writing at least one "happy path" integration test at least for the main scenario (or several).