Data privacy for test environments
You should check out the Anonymizer extension.

A word of warning - make sure that outgoing email is disabled!  You don't want any of your CiviRules etc. being triggered and sending out emails.  I saw a colleague who had CiviCRM WordPress Profile Sync installed, which meant that changing the email address in Civi changed the email in WordPress - which sent out a "your email address has been changed" message to everyone who had a login...