Google is now showing AMP implementation errors directly in the search results to the site owner. The error will show in the search result snippet and be a hyperlink to the help documentation on how to fix the error. Google is aggressively pushing AMP adoption for webmasters, recently announcing they are expanding AMP into the core mobile search results.
Jon Henshaw posted this screen shot of the AMP error notification he saw in the desktop search results:
Google also offers site owners warnings if their site is not mobile-friendly, so this is an obvious extension of that.
The AMP warnings to site owners read “Your page has AMP implementation errors.”
Google has confirmed this is not a test.