Test Mode for Adsense Ad code?

I have a wordpress site on which i am showing adsense ads. I came across a plugin that i really like would like to use to show my ads with.

The plugin injects the adcode after the first paragraph in the content. So as an input to the plugin i will have to provide the adcode. Using placeholder images is not an option.

I wish to tryout this plugin first on a localhost test wordpress setup, So i was wondering how to i make adsense serve test ads.

I did find a few articles on the web saying that if i put google_adtest = “on”; value as the first line of my adcode adsense will server test ads. I also read a contradictory article saying not to modify the adcode. So i am in a dilemma here.

I did not find any documentation regarding this in the official adsense site?

So kindly provide officially documented ways to test adsense ads with links to the documentation.

-Thanks