In the previous section we looked at Kernel tests and said that they are basically integration tests that focus on components rather than interactions with the browser. In this section, we'll go one level up and talk about the fully-fledged Functional tests, otherwise called browser tests (from the name of the base class we need to extend).
Functional tests in Drupal 8 use a simulated browser (using the popular Mink emulator) that allows users to click links, navigate to pages, work with forms and make assertions regarding HTML elements on the page. What they don't allow us is to test JavaScript-based interactions (see the next section for those).
In Drupal 7, Functional tests were the most common type of tests used, most classes extending from Simpletest's WebTestBase class. But in Drupal 8 we have the Drupal\Tests\BrowserTestBase class which is...
