Just run composer install and you will get phpunit and dependencies in place.
PHPUnit, Rector and PHPStan are automatically ran by GitHub Actions however you can also run them manually as composer scripts.
Type composer run to get into the interactive console and try them out.
Contributions are really welcome. But it saves time for both sides when at least the phpunit and phpstan runs do not fail.
We will not accept newly added fields/features without full test coverage in the PR.
So please, before committing, always run:
composer run phpunit
composer run phpstan
composer run rector