It’s actually easy to test. Load up any spool. Once the print has started, snip the filament between the spool and the ams inlet. This simulates the spool running out.
The run-out feature has to be enabled on the printer.
When you send the print from Studio you can pick what slot is being used. Here mine defaulted to A4 (The full spool) but you can pick A2 to start the print from.
You can verify what slot is set for backup by clicking on the “Auto Refill” text.
Here is a link to a thread if you want to autofill with a different color of filament.