Thanks to some work by MGlaman and KarinG and others, some integration with the Mink/Behat front-end testing framework is now available for you to use to write automated tests. Does it replace regular phpunit? No, you should still write regular tests too. But let's take a look at what it can add.
What are front-end tests? They're tests that automate controlling a browser to fill out fields and click on buttons, as opposed to the usual back-end tests that might check the output of a function.