Net Tuts+ JavaScript Testing From Scratch

This likely isn’t the first tutorial on testing that you’ve ever seen. But perhaps you’ve had your doubts about testing, and never took the time to read them. After all, it can seem like extra work for no reason.
This tutorial (with screencasts) intends to change your views. We’re going to start at the very beginning: what is testing and why should you do it? Then, we’ll talk briefly about writing testable code, before actually, you know, doing some testing! Let’s get to it.