The Test Suite is not demonstrating removal of a DC component, as there is no way to identify the AC component in any of the tests! For example, Test 3 has x = 0:100, and from this we are supposed to obtain signalMean = 50. But without any observations to show that at earlier & later times the signal is decreasing with time, like x = [2 1 0:100 99 98], we have no way to know that more observations wouldn't have revealed, say, x = [2 1 0:100 101 102], for which signalMean = 51. And indeed we could get any arbitrary signalMean based on the limited observations in this Test Suite.