Start testing your app with Casper.js
blog.codeship.io
blog.codeship.io
I love the idea, but I'm a bit worried that it's just webkit. Aren't all the other browsers important too? This is why I feel that Selenium still has a place, even though I agree that Casper is easier to use. Perhaps browserling is an appropriate answer?
I don't mean to disrespect CasperJS or PhantomJS, they're certainly wonderful tools, and any final automated functional test like this is infinitely better than none, but it's bad enough that people are developing for Webkit, do we really have to make it explicit by only testing on Webkit? ;)
The point of the parent is to test on multiple browsers.
Most likely your front-end/UI uses other libraries to handle cross-browser issues so your automation tests will focus on the functionality of the application as opposed to catching cross-browser bugs or performance issues.
The problem that PhantomJS solves is to run headless browser which is very useful for organization that runs their build/tests on their CI-server and would prefer minimal setups (as opposed to have "testing-labs" like the big guys [yahoo, ms, google]). That itself reduces the cost of development/testing cycle.
JsTestDriver and Test'em 'Scripts do too. (I haven't tried Test'em yet, but that's what I hear.)
Granted, these aren't tools for functional testing like Selenium and (apparently) CasperJS, but functional tests are something you want to minimize as much as possible. They're slow-running and brittle.