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