When to enable ads test mode?

can anyone pls tell me when do i need to enable the ads testing mode, because I was working on my first game for the last 7 or 6 months and now it’s almost ready to be published that’s why i need to test its ads first…I don’t know if I need to let the test mode enabled when testing the game on my phone or not ?

If for google play you better have test on because they get pretty cranky if they think you’re watching your own ads for profit.