There was four stages; first the initial application followed by a SJT followed by an awkward online video interview and finally the Assessment Centre.
The Assessment centre had three main parts: A demo, Technical & Competency interview and finally the group exercise. The deom was pretty cool and enjoyable using oculus to see around some of thier main sites. The technical and Competency interview had two main assessors with the usual "tell me about a time when..." format questions. The technical questions were mainly basic engineering principles, depending on what your engineering discipline is. The assessors were very friendly which helped a lot to feel calm throughout.
The group exercise was to make a bridge using some basic materials. Make sure you try engage as much as possible as you do get some competitive people in this session. Try bring about new ideas and keep a track of the time.
Found out two weeks later I got rejected, but it was an overall good experience.