It's all computer based now. I remember they had just introduced the CLAN test when I went through. As a test of capacity it must have been quite good because the amount of muttering and swearing that could be heard around the room was quite amusing.
If memory serves it was a series of vertical coloured blocks with same coloured circles moving across the screen at different rates. When the red circle passed over the red block you pressed the red button and so on - I think there were 4 colours IIRC. Then on top of that you had to do mental arithmetic problems; again IIRC the question came up at the bottom of the screen and you had to select the correct answer a,b,c,d (or something like it). And then finally there was memory test element where a string of letters / numbers came up and you had to memorise them and then either type the string back in again when prompted or select the right one from a choice. All the elements were in themselves very simple, but start to do them all simultaneously and it got interesting. Speed things up and it got really interesting.