it("Should show image preview for URLs with known image extensions", function () {
                checkImageDataAtPos("http://example.com/image.gif", 194, 20);
                checkImageDataAtPos("http://example.com/image.png", 195, 20);
                checkImageDataAtPos("http://example.com/image.jpe", 196, 20);
                checkImageDataAtPos("http://example.com/image.jpeg", 197, 20);