Is there a way to test if a firewal (AFwall) l is blocking a specific app? I installed AFwall+ to block internet connection for my keyboard. Is there a way I can test if this is actually working? The keyboard is Swifkey.
Android setting has an option named 'Data Usage' where you can see per app data consumption. Compare consumed data on two instances to make sure it is not using any Internet.

PS: IMO If you've Xposed installed then LighteningWall could be a better option.