The four compass points can be abbreviated by single-letter strings as "N", "E", "S", and "W". Write a function turn_clockwise that takes one of these four compass points as its parameter, and returns the next compass point in the clockwise direction. Here are some tests that should pass:
test(turn_clockwise("N") == "E")
test(turn_clockwise("W") == "N")
You might ask "What if the argument to the function is some other value?" For all other
cases, the function should return the value None:
test(turn_clockwise(42) == None)
test(turn_clockwise("rubbish") == None)