🟢 DELIVERED - Define cohorts using existing cohorts (i.e. nesting cohorts)

I want to make a cohort that is based on, and dynamically updates with, an existing cohort.

For example. I have a defined Test Users as those who meet some criteria, but have also had to add a number of test users as one offs. 

I’d like to make a derived cohort called Test Users - Activated that simply adds another criteria on top of that cohort in a way that stays in sync if I have to manually add another user to the original Test Users cohort. 

If I’m approaching this totally wrong, someone please let me know a better way to manage this!