RAT/ADG testing is a normal check on the Challenger series. Normally requested by the engineers before taking the aircraft in for major maintenance.
There is a full checklist provided, to ensure that you land with sufficient electrics to power the antiskid. Antiskid on the Challenger works down to 12kts.
Some great marks on the runway in Biggin upon landing yesterday....even better were the wheel rims......nicely flattened! Apparently a JETS engineer was onboard too!