How to clear placement test

Recently, I was talking with one of my friend who shared this interesting thing with me. He has seen few of his juniors(from CS background ) struggling to clear campus placement tests. Majority of them fail during the coding round and a few in aptitude. Cheating is quite common during campus placements is what he shared. He has also seen non CS/ECE/IT background folks pulling some tricks during this time and are somehow able to clear the test. No idea how they do it without getting caught. But the biggest question I had was, how are CS folks not aware of such thing? and what are those tricks/methods/art they let's you do it so smoothly???