I was initially contracted by a third party company to work in IBM. The interviewer is usually a team leader of the unit you're gonna work on. If you're gonna be contracted by IBM, however, the process is different. There's an exam that will test you on math, logic and English (1st phase). The 2nd phase (if you pass on the 1st) have the process called "group dynamic" (not sure if this is the right term) where an HR recruiter will provide you a scenario and request a random stuff (draw a flag that represents your skill, personality), make a plan for a given task, etc.

3 rounds of technical assessment, one manger round and completed , in technical round all kind of question was asked and verified about the technical and leadership skills.