If you are testing your new website layout, you might be reloading your website pages 
again-n-again. And if these pages contain Google Ads, each time your reload your page, you make a request to Google Ads Server for a new set of ads.
Certainly Google is unaware that you are testing your website and it might even penalize your account for "click-fraud" since the IP requesting ads remains same. And if in the worst-case scenario, you might accidently click on your own ads. And these extra "ad impressions" will also chance your CTR data.
One simple way to avoid this serious problem is to remove the Adsense code altogether from your page before testing. But this may not be the best solution as your Google Ads are an important part of your layout. So here are a few simple but effective workarounds: Precautions before testing Google AdSense on your website - Digital Inspiration