Google has quietly added a "preview" button to the Google Structured Data Testing Tool for some types of structured data - not all. For example, if you bring up the results for a video post here, such as this, Google will show two types, a NewsArticle and VideoObject.
For the NewsArticle, Google offers the preview button but not yet for the VideoObject.
Here is what the preview button looks like:
Here is the output:
I did not test all the data types to see which has and which does not have the preview button. But I know the NewsArticle has, Recipes, Products and I am sure many others.
Ramesh Singh first spotted this and posted it on Google+.
Forum discussion at Google+.
