Test the setting of the -webkit-image-set function. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". Single value for background-image : url(http://www.webkit.org/a) 1x PASS testComputedStyle("background-image", "-webkit-image-set(url(http://www.webkit.org/a) 1x)") is "-webkit-image-set(url(http://www.webkit.org/a) 1x)" Multiple values for background-image : url(http://www.webkit.org/a) 1x, url(http://www.webkit.org/b) 2x PASS testComputedStyle("background-image", "-webkit-image-set(url(http://www.webkit.org/a) 1x, url(http://www.webkit.org/b) 2x)") is "-webkit-image-set(url(http://www.webkit.org/a) 1x, url(http://www.webkit.org/b) 2x)" Multiple values for background-image, out of order : url(http://www.webkit.org/c) 3x, url(http://www.webkit.org/b) 2x, url(http://www.webkit.org/a) 1x PASS testComputedStyle("background-image", "-webkit-image-set(url(http://www.webkit.org/c) 3x, url(http://www.webkit.org/b) 2x, url(http://www.webkit.org/a) 1x)") is "-webkit-image-set(url(http://www.webkit.org/c) 3x, url(http://www.webkit.org/b) 2x, url(http://www.webkit.org/a) 1x)" Duplicate values for background-image : url(http://www.webkit.org/c) 1x, url(http://www.webkit.org/b) 2x, url(http://www.webkit.org/a) 1x PASS testComputedStyle("background-image", "-webkit-image-set(url(http://www.webkit.org/c) 1x, url(http://www.webkit.org/b) 2x, url(http://www.webkit.org/a) 1x)") is "-webkit-image-set(url(http://www.webkit.org/c) 1x, url(http://www.webkit.org/b) 2x, url(http://www.webkit.org/a) 1x)" Fractional values for background-image : url(http://www.webkit.org/c) 0.2x, url(http://www.webkit.org/b) 2.3x, url(http://www.webkit.org/a) 12.3456x PASS testComputedStyle("background-image", "-webkit-image-set(url(http://www.webkit.org/c) 0.2x, url(http://www.webkit.org/b) 2.3x, url(http://www.webkit.org/a) 12.3456x)") is "-webkit-image-set(url(http://www.webkit.org/c) 0.2x, url(http://www.webkit.org/b) 2.3x, url(http://www.webkit.org/a) 12.3456x)" PASS successfullyParsed is true TEST COMPLETE