On Wikipedia, the Google Test is looking something up on Google. This can be:

• as a quick and rough to check that something actually exists (we get articles about things that don't... personal theories, personal fictions etc)
• as a quick and rough check for copyright. When a new or IP user submits a large chunk of text, it's a good idea to be mildly suspicious and "Google test" a few 10-word or so segments.