As I am learning the test seems to measure how you are coping at the moment, and so the results for me at least vary every time i take it. It isnt a diagnosis tool And of course no online test can really tell you how you are feeling. Its much better to get a professional opinion, the test is merely a very useful tool to check what you areas you need to work on.
Also I find people show depression in different ways, it took a while for a psychiatrist to realsie i was actually very depressed as I mask it quite well. Though there normally are the obvious signs, if you are having difficultly functioning in every day life, ie energy levels, concentration and motivation and it continues for a while then you probably need to see someone.