Cloning a site in WPEngine
Your error message has a path with the word "live" in it (/nas/content/live/etc) which suggests that the civicrm_root value hasn't been changed on the test site.

civicrm.settings.php is the equivalent of wp-config.php - you need a separate version of this file for your live and test sites.  Please review your test site's civicrm.settings.php - not just to fix the civicrm_root but also the database settings, base URL, etc.