Once you start writing tests, you can't stop

Once you start testing/TDD, you can't go back

Once you start writing automated tests or doing test-driven development, you can't go back to not doing it.

When adding a new feature, you'd need to test every situation and use case manually in a browser or command line - and, very likely, do so multiple times.

When fixing a bug, you'd need to follow the exact steps to replicate it and see it before attempting a fix. Again, you'd also need to test it manually.

Also, because it passes a manual test, there's no guarantee it won't break unexpectedly in the future.

While refactoring code without tests, bugs and regressions could be introduced as there's no test suite to run and ensure they're still passing.

Here's the thing

When you're used to writing tests and doing test-driven development, you get used to the quick feedback loops and the confidence to make changes.

It's easier to create a test that proves a bug exists and shows it's fixed because the test passes.

Once you have these things, you can't stop and go back to not having tests.