Phpunit mink

```
$ DOMAIN=d8-phpunit.dev core/vendor/bin/phpunit -c core --testsuite functional --group modern --debug --testdox

PHPUnit 4.1.3 by Sebastian Bergmann.

Configuration read from /Users/nickschuch/projects/personal/phpunit-d8/app/core/phpunit.xml.dist

Drupal\simpletest\Tests\BrowserTestBase
 [x] Go to
```
What is this used for?