Can the test reveal how heavy the smoker is or does it just indicate if the person smokes weed? I suspect that my parents might test me in the future, so I need to know for my detox.

...it just indicate if the person smokes weed‎‎‎‎‎

There are probably some more advanced tests which determine the quantity of cannabis metabolites [is that the right word?] in the blood, but if it's your parents testing you then it'll be a simple test which just shows it's in your blood.

(I could be wrong about the first bit though)

I think it basically will only tell you whether you've been smoking weed or whether you haven't. I don't think they could get an accurate reading of how much you've smoked.

Urine test determines the presence of THC metabolites in your urine. More advanced urine tests will tell exactly how much of the metabolite by ng/ml is in your urine. If you smoke just once the metabolites leave your system relatively fast, if you're a heavy smoker then you will have a huge amount built up.

Blood tests are the same except they can detect the actual THC in your blood therefore know that you smoked very recently.

ya i had to take a more advanced test at this rehab center and they said my levels of thc stayed the same the entire 2 -3 weeks i was there. lol

"Lab tests" as I have heard them referred to, give you a THC level of 1-200. This would determine whether or not you smoke regularly.

I bet it is expensive as fuck, but someone could do a hair test on you. You would be able to see every drug you have taken within the life of that hair, and how many times you have used a drug.

Moral of the story: Keep your hair short. Actually, they can take hair from anywhere on your body, so its best not to have any hair.