http://w3.org/TR/css3-fonts/#font-stretch-prop

WARNING: this test will only pass if the font family in use has width-variant faces. Therefore, a user agent can support font-stretch and still appear to fail this test.

NOTE: this test uses faces of SwitzeraADF, assigning various individual faces to various stretch levels (and cheating by using a light condensed face to substitue for “ultra-condensed” and a bold extended face for “ultra-expanded”). If the following paragraphs are in a serif font, then the font has failed to load. If they are sans-serif, then the font has most likely loaded and the test should be valid.