PHPUnit has been upgraded from 4.1.0 to 6.2.x in Magento 2.2.0-RC1.8

News
, , , , ,
1

https://github.com/magento/magento2/blob/2.2.0-RC1.8/composer.json#L76-L76

https://github.com/magento/magento2/commit/df7278a2