How can I tell if my drink is really sugar free? [closed]

I suffer from diabetes mellitus and when travelling, I always try to avoid sugar in food and drinks. I prefer home made food, and when at a new restaurant, I generally skip the dessert unless I'm sure it is sugar free.

With drinks anyway I have troubles sometimes. It happened to me a few times when travelling that I ordered a light coke/pepsi, etc. and was served normal coke instead. From my experience this typically happens because the waiter misses the word "light", maybe because their english is not so good or because they are in a hurry, or don't have light coke at all but don't want to disappoint the customer, or simply because they don't care. Coke with and without sugar have a similar taste but normal coke has a stronger aftertaste and sticks to the mouth and teeth more than light coke does. I can tell the difference, but only after taking a few sips of the drink. Sometimes I also notice sugar in sugar-free warm drinks, like coffee and tea drinks, albeit less frequently. It's not that a few teaspoons of sugar would kill me, but this unclarity bothers me.

Is there a way I can tell if a drink contains sugar before actually drinking it?