All you need to do is install the package, and you're good to go:
composer require ssch/typo3-rector-testing-framework --dev
To add a set to your config, use one of the classes from sets under Ssch\\Typo3RectorTestingFramework\\Set\\
class and pick one of the constants:
use Ssch\Typo3RectorTestingFramework\Set\NimutTestingFrameworkSetList;
use Ssch\Typo3RectorTestingFramework\Set\TYPO3TestingFrameworkSetList;
use Rector\Config\RectorConfig;
return static function (RectorConfig $rectorConfig): void {
$rectorConfig->sets([
NimutTestingFrameworkSetList::NIMUT_TESTING_FRAMEWORK_TO_TYPO3_TESTING_FRAMEWORK,
TYPO3TestingFrameworkSetList::TYPO3_TESTING_FRAMEWORK_7,
]);
};