}

		piper, pipew := io.Pipe()
		pb := bufio.NewScanner(piper)
		go sng(pipew, fn, img)
		defer piper.Close()

		// Read the .sng file.
		sf, err := os.Open("testdata/pngsuite/" + fn + ".sng")
		if err != nil {
			t.Error(fn, err)
			continue
		}
		defer sf.Close()
		sb := bufio.NewScanner(sf)

		// Compare the two, in SNG format, line by line.
		for {
			pdone := !pb.Scan()
			sdone := !sb.Scan()