The introduction of Behat 3, and the subsequent release of the Behat Drupal Extension 3, opened up several new features with regards to testing Drupal sites. The concept of test suites, combined with the fact that all contexts are now treated equally, means that a site can have different suites of tests that focus on specific areas of need.
Behat is a PHP framework for implementing Behavior Driven Development (BDD). The aim is to use ubiquitous language to describe value for everybody involved, from the stake-holders to the developers. A quick example: