How exactly do the addiction tests work?

In the RAW it says "every time you use an addictive substance during (11-Addiction Rating) weeks in a row, make an addiction test." (SR5 page 414) What exactly does that mean? It's confusing. An example would be helpful.

the rules are about as clear as mud. they're also contradictory, and probably basically boil down to "if you use any drug whatsoever in any amount ever, you'll probably get addicted with no realistic chance of avoiding it no matter what you do, and then proceed to spiral downards to burnout, with the only question being how fast it will happen" (i say probably because hey, clear as mud and contradictory, remember?)

or, in other words... you're probably better off either ignoring drugs entirely, or writing your own addiction rules.

In the end: in less then 10 years the earth population would only consists of some millions of health fanatics - because the 7 billion men, women and children who ever tried to drink or smoke would have been killed by the almost-instant-addiction and the almost-automatic death some years later. Alcohol and cigarettes are as deadly as the ghoul virus rules in SR4

As Jaid said: ignore the addiction rules, go for common sense.

SYL

Ok, so you like to take Long Haul (Addiction Rating 2, Threshold 1).
If you take Long Haul for (11 - Rating 1 = 10) weeks, you make an addiction test. Long Haul's addiction type is psychological, so you roll Logic + Willpower against the Threshold 1. If you succeed, you are fine (or your addiction stays the same). If not, you get a mild addiction (or your addiction becomes more severe). The Threshold can be reduced by one for each week you don't take the substance, so skipping the last week (and if you are addicted already enduring withdrawal symptoms) makes the test easier (in this case it gets reduced to 0).

Now, if you are a regular runner that likes to take Jazz (Addiction Rating 8, Threshold 3) it's a bit more dangerous:
If you take Jazz for (11 - Rating 8 = 3) weeks, you make an addiction test. Jazz' addiction type is both physiological and psychological, so you roll Logic + Willpower and then Body + Willpower against the Threshold 3. Fail either one, and your addiction starts/gets worse. Again, the Threshold can be reduced by one for each week you don't take the substance, so skipping the last week (and if you are addicted already enduring withdrawal symptoms) makes the test easier (in this case it gets reduced to 2).

TL;DR: Soykaf (Rating 1, Threshold 2), Long Haul and Alcohol (Rating 3, Threshold 2) won't kill you in years, but Nitro (Rating 9, Threshold 3)? Chances are it will. Rightfully so.

So you're saying they have to make the addiction test at the end of the (11-rating) weeks, with the threshold decreasing one per week after the last dose? What if someone took fourteen shots of novacoke (rating 7, threshold 2) over the span of two weeks, then went cold turkey for two weeks? They wouldn't have to make an addiction roll? But if someone uses it once a week, they'd have to make a check with a threshold of 2 the month after they first started using?

See the problem yet?

Dont have the book in front of me. But I seem to remember that taking it more frequently screws you by making you either do an addiction test sooner or making it harder to resist (or both)

Nothing official, but each time a PC takes a dose, I'd subtract the addiction rating from the weeks left until an addiction test takes place.