Best way to test it is how my insulin pump doctor and nursing team taught me.
1st things 1st, get you Basal/ background insulin right.
To do this, test your levels, if they are good, go carb free for several hours, check again and if your levels are similar ( not more than 1.0mmol a difference) then do the same the following day/ night at the same time. Eat 10g of carbs then leave it the same amount of hours making sure your background insulin was the same as the day before, also make sure your activity/ exercise is similar or the same as the day before, this should help you get your background right.
Now you have eaten the 10g of carbs waited a few hours ( after following the above guidelines) re test your levels and you should have your answer.
To bring your sugar levels back to range:-
Go carb free and also make sure your background / basal levels are correct and test. Based upon your result take 1 unit of fast acting insulin if it is near your target but not quite. A few hours carb free later the test and see where your levels are at