Hello,
Yes, I turned off test mode. I checked debug APK and tested both with test mode on and test mode off and it was showing ads perfectly.
An interstitial ad is created on the level select screen (which is the screen with the submarine in it).
The loaded interstitial ad is shown once every three times when the player goes back to the level select screen.
Here's a link to the game: play.google.com/store/apps/details