1st stage was a two-part test. It contained rather standard and easy problems. 2nd was an interview with a researcher. Questions were more difficult but solvable. In general, both were strictly technical. Problems were similar to those given as examples on their website.

Test (20 question for 90 minutes if I recall correctly), then three rounds of interviews. Got rejected after the second round (which alone consisted of 3 interwiews). I believe third round would have been on site.