AdWords converted the "Rotate Ads Evenly" setting to "Optimize for Clicks" which will grossly distort Ad Testing. Go to Settings/Ad Rotation and select "Rotate indefinitely - will deliver ads more evenly for an indefinite amount of time" When you run two test ads inside an Ad Group, you want to run both ads at least 200 hundred times for statistical accuracy. If we don't change the default setting "Optimize for Clicks", AdWords would stop running one of the ads before both ads had run 200 times. So AdWords could stop running the better ad, before the test is complete.