The biggest downside to Screw Unit is the project momentum. The original authors don’t seem to be doing much with it these days and it’s difficult to find a source of truth. So in the mean time I look to Trotter Cashion’s fork for stability since I know he’s used it for testing a number of production apps. His version also has a better Stubbing/Mocking toolkit than what Screw Unit originally comes with.
JsTestDriver: Written by Java developers for Java developers. And as best I can tell offers no support for asynchronous tests. The browser capturing is cool, and I’ve seen some interesting advances in the tooling for this framework, but it doesn’t seem worth the Java culture that comes along for the ride.
JsUnitTest: This is a fork of prototype’s test suite but with the prototype dependency removed. I was excited about this early on, but had a lot of trouble getting it to run correctly across all browsers. The runner pages also require a fair bit of boilerplate which is a big turn-off.
JsUnit: I’ll mention this purely for historical reasons. Don’t use it. It’s old, crufty and I’m pretty sure they spent more time on their logo than they did on the test runner. We started using this on our project originally and quickly grew to hate and ignore it.