I am not sure what you mean by testing a domain name... I am assuming you want to see if one brand name works better than another... considering the cost of buying a domain name is less than $10 a year, I would just buy the ones you are interested in and try promoting both with adwords...

In general it is a violation of google's TOS if you dont have added value content on your site... so I wouldn't advertise it on google if you are just testing a domain name... I would make sure to have actual content and a functioning website...

I would recommend using Google Consumer Surveys to do a poll of two different names, but make sure to register both domain options or someone might steal them from under your nose... http://www.google.com/insights/consumersurveys/home?gclid=CKG_8Kfsv7oCFUfZQgodhS8Azw