Yes, the test would show the true results. The tricky part is that you may not suspect that you are under the influence of alcohol and think that you are absolutely sober, even though you have a certain concentration of alcohol in your blood. This is due to increased tolerance to alcohol – the more you drink, the more tolerant you become.
The same thing can happen with drugs, by the way. In course of time, you get used to drugs, your tolerance to drugs increases, so you need to consume more drugs to feel the effects of high. You might not even realize how your drug dosage increased in course of time. Indeed, the feelings when using drugs can subside while the concentration of the drugs in the blood, as you consume more, increases.