CasperJS is a JavaScript testing framework built on top of PhantomJS (WebKit) and SlimerJS (Gecko). It provides a range of features for functional navigation, page status monitoring, network monitoring, screen capture, and data scraping. CasperJS allows assertions, making it easier to track failed tests. The API has an extensive collection of features, including the tester module, which is used for unit and functional testing assertions. CasperJS can be integrated into continuous integration pipelines to test HTTP status codes, page titles, and screens. It can be run from the command line using `casperjs test <test_file>`. The framework has excellent documentation, making it easy to learn and use. Headless browser testing serves a purpose in the delivery chain, providing an additional layer of testing beyond traditional real browser testing.