It may be a squeamish ossifrage[1] or a seraphim proudleduck[2], which is to say that it was an artificial phrase chosen to be extremely unlikely to occur naturally. In this case, the purpose is likely for QA. It's much easier to QA behavior with a special-purpose but otherwise unoffensive phrase than to make your QA team repeatedly say allegedly offensive things to your AI.
I think the EICAR test file [1] is more apt. Rather than passing around actually malicious files as part of your tests, it's better to just have it recognize an innocuous and unlikely pattern as malware.
