Acceptance Test-Driven Development is an Agile technique that extends the test-first approach to the development of the front end of an application. The mechanics of Acceptance TDD are clear: first you write a test which defines the goal of your development, which is basically the feature you're adding to your application. As with all TDD variants, this test must fail.
With the help of the Zend_Test component, your tests can execute through the full MVC stact of your application (including views) to check to see if the resulting content matches certain criteria. He includes a few code examples showing content searching (contains), validating the query string and checking for a redirect.