Test for handling of url() that can be an image or an element

The first test has mask-image: url(mask-url-image#myMask) which points to a circle mask inside an SVG file (whose primary image is a square):

The second test has mask-image: url(mask-url-image#nonExistentMask) which points to a nonexistent element inside the same SVG file (whose primary image is a square):