It's hard to tell what is generally the best way to test web apps. There are quite a lot of tools already and probably apart from choosing the right tool, you'll need to think about what you should test, where, and how.

We'll mostly talk about unit testing because it can be used for both web and standalone apps. Then, in the context of AngularDart, we'll mention the so-called end-to-end tests with Karma and Protractor. We're not able to cover everything in this chapter, so if you want to know more about testing in JavaScript and in the browser, take a look at the master's thesis of Vojtěch Jína, a current employee of Google, who has been working on AngularJS for more than 3 years: https://github.com/karma-runner/karma/raw/master/thesis.pdf.