While supposedly on the down low, Facebook Inc (NASDAQ:FB) is currently testing a new feature with select group of marketers that allow users to share offsite ads on the social networking site.

According to Mashable, while marketers and advertisers have usually either bought ad units or Sponsored Stories from the Facebook ad platform, the new feature will enable them to create advertisements that aren’t on Facebook shareable via Open Graph.

Buzzfeed.com was the source that essentially let the cat out of the bag for testing thanks to a “Featured Partner” post for Hidden Valley Ranch. This one included a Facebook Share–not the norm for BuzzFeed.

Facebook Inc (NASDAQ:FB) confirmed the testing to Mashable and said the offsite ads will be shared on it.

Neither details of the test’s size nor the number of partners has been disclosed.

What’s interesting about the test is that sharing ad units straight to Facebook through the Open Graph has been in violation of the company’s Terms of Service. Now Facebook may be trying to work with advertisers to have offsite content on it sans the traditional ad unit.

It makes sense to have BuzzFeed as a guinea pig. The company has previously said about 50 percent of its mobile traffic is from Facebook. And one of its top revenue drivers comes from producing shareable content for various brands.

By working with a brand–in this case Hidden Valley Ranch–content can be created that will go viral, appealing to BuzzFeed’s demongrahic. Not a bad thing since they’re viewed as trendsetters.

Furthermore, this type of sharing unit created by Facebook (accessible directly from the homepage) doesn’t have people clicking to another link; this should allow for easier sharing.

So what does the shared unit look like?

Mashable reported that it looks similar to other shared Facebook content pieces but since it comes from an app it does not include the “reshare” button on Facebook. Users can either “like” or comment on it but should they desire to share it, they will need to return to the main site and then click on “share.”

By doing so, Facebook traffic returns to the initial advertising source.

This isn’t anything new as social platforms have been experimenting with additional social ad units for a while. In October, Google (NASDAQ:GOOG) begin placing +1 buttons on select display ads to assist with a change in viewing advertising.

google plus 1 ad

In 2010, Digg tried it with “Diggable” banner ads.

Digg Ads

The difference now is inventory comes from marketing partners not Facebook. How this turns out for the company with these unit types remains to be seen but there could be lots of opportunities for marketers.