By lauriii on
Change record status: 
Published (View all published change records)
Project: 
Drupal core
Introduced in branch: 
8.0.x
Issue links: 
https://www.drupal.org/node/2350823
Description: 

Earlier Drupal 8 releases (including beta 3) were using Stark as the default theme for the functional tests. Since #2350823: Use the Classy theme in the Testing profile Drupal 8 (starting from beta 4) is using Classy as the default theme for the functional tests.

If your test uses Stark, it will now break unless you explicitly install it: \Drupal::service('theme_handler')->install(['stark']);

Impacts: 
Module developers