Look at it this way: you must be testing code as you write it anyway. There's really no other sane way to do it. You make a change, you load the page and see that your change worked, or you call your new function from an interactive interpreter.
Smart automated testing just takes all that extra test work you're already doing and saves it as you go along.
No need to try to invent extra things to test. You just test what you would have tested anyway by hand.
Smart automated testing just takes all that extra test work you're already doing and saves it as you go along.
No need to try to invent extra things to test. You just test what you would have tested anyway by hand.