When I applied 4ish years ago I failed on the cube test.
I re-took it a couple of months ago and passed.
If you can't get it AT ALL, then you are on a bit of a loser.
However if you can see some tests and look at the answers and then work out why that one is the right answer, you may find you understand it. Most of the tests are easy to grasp, IMHO, very quickly, however the cube one takes a bit of getting used to... Problem is almost all the ATC tests are dead easy *IF* you have unlimited time to do them in... The problem is you don't, it is a constant race against the clock (obviously that is the idea!) and therefore it is important that you can grasp what you have to do, and understand it in double quick time.
Cheers,
James.