Private Test
Test user property and private cache
Session User
https://developers.google.com/apps-script/class_session
active user vs effective user
Private Cache
https://developers.google.com/apps-script/class_cacheservice
"Private caches are private to the current active user and script.
They can be used to store information specific to that user."
User Properties
https://developers.google.com/apps-script/class_userproperties
" Key:Value pairs associated with this user."
User property is always associated with the effective user