The QaFoo blog has a post to their blog introducing page objects and how they're useful in functional testing to help provide a "decoupling" from the actual frontend.
A while ago we wrote about writing acceptance tests (end-to-end tests) with Mink and PHPUnit. While this is a great set of tools for various applications such tests tend be susceptible to changes in the frontend. And the way they break is often hard to debug, too. Today I will introduce you to Page Objects which can solve some of these problems.
The basic idea behind a Page Object is that you get an object oriented representation of your website. The Page Objects maps the HTML (or JSON) to an object oriented structure you can interact with and assert on. This is more initial work then than writing tests with PHPUnit and Mink directly, but it can be worth the effort.
They use the Mnk testing tool to simulate a browser and some previously shared functionality to lay the foundation. From there they write up a first test using a "Login" page object and processing the username/password handling of the page. They show how to implement a custom page object with a bit of additional logic and put it to use in processing the request. They also include an update when, for example, a site is switched from Twig templates to a React.js component and how the Page object would need to be refactored for the update.