Hey Matthieu! Airtable formulas only have access to one row of data at a time. So a formula executing in one row has access to any column values it needs, but not any other rows. The exception is the functionality that linked records/lookups afford, but I don’t think that helps in this case.
The alternatives you’re left with are probably:
- filtering, sorting, or grouping your list by date ranges
- write a script to populate TEST whenever you click a button
- rig up a third party integration that automatically scours for updates to the base, and updates the TEST column as necessary
Best of luck!