As advocates for the use of modern images formats, we believe tools should accept more performant image formats if we expect users and developers to fully adopt them. In addition to the previously mentioned AVIF and WebP, HEIC/HEIF is tested for. HEIC/HEIF not only reduces file size by ~50% compared to JPEG, but with iOS 11, it now is also the default image format for more than 50% of cell phones in the west. Making these new formats as ubiquitous as their forebearers are today necessitates them being accepted.
The test is simply if each format is an accepted as source file for optimization. This is, by nature, custom to each tool and service.