Syntax:

\Drupal::service('page_cache_kill_switch')->trigger();

Example on a controller:

Install via composer

composer global require drush/drush:10.x

Install Apache 2 server

sudo apt install apache2

Install MySQL Server

sudo apt install mysql-server

Create a Drupal 9 project with composer

Error N°1 : PHPunit not found

If uou have a message like : Add Phpunit via composer

CAUTION : PHPunit Version >= 8 is not compatable with drupal, so use the 7

composer require --dev phpunit/phpunit:7