\Drupal::service('theme_handler')->install(['classy']);
$this->config('system.theme')->set('default', 'classy')->save();
- drupal_set_message('An error occurred', 'error');
- drupal_set_message('But then something nice happened');
+ \Drupal::messenger()->addError('An error occurred');
+ \Drupal::messenger()->addStatus('But then something nice happened');
$messages = [
'#type' => 'status_messages',
];