Just run composer install and you will get phpunit and dependencies in place.
PHPUnit, Rector and PHPStan are meant to be run by CI 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 travis builds do not fail. We will not accept newly added fields/features without full test coverage in the PR.