You mean to tell me, if I go visit China they may _force_ me to do a drug test?
It happens but it's still pretty rare
The scary thing is that if you are tested positive I believe you would end up in jail for a month before getting deported, even if you consumed legal drugs in your country (ie cannabis)
If you deny to take the test you would definitively be in trouble, at best you would get deported
This would probably happen in many countries. If I were to smoke cannabis legally and this showed up in a drug test in the US (e.g. stopped while driving) you could also be arrested as a foreigner. With many drugs the effects are not as clear as with alcohol, a test can show up positive even though effects are long gone.