Just test. Below 3 km, slower than 800 km/h. Routine test for all new fighter jets with ejection seats. GLIC, a testing installation near city of Astrakhan, is funny place. One of its test pilots, former Yak-38 VSTOL driver of Pacific Fleet, told me how they strafed a mock T-72 tank from Su-34 with 30-mm gun, elaborating methods to hit the engine compartment. It turned out that it is better to fire being descending on the loop, thus allowing several shells to dig the soil and after this several next ones hit the mark. Since it is extremely doubtful that in fact medium bomber Su-34 will ever strife the ground in CAS fashion, I think no line squadrons will get such training, but GLIC people want to know what airplane can do and what cannot, and sometimes it resembles some activity just for fun?