You find guides how to develop AppShell if you want to contribute to AppShell itself.
To test against PHP 8.0:
docker-compose run appshell_test_php80 sh -c 'cd build && vendor/bin/phpunit --stop-on-error'
To test against PHP 8.1:
docker-compose run appshell_test_php81 sh -c 'cd build && vendor/bin/phpunit --stop-on-error'