public String compareFiles(String filenameOK, String filenameOUT) throws FileNotFoundException {
        Scanner sOK = new Scanner(new File(filenameOK));
        Scanner sOUT = new Scanner(new File(filenameOUT));

        while (sOUT.hasNext()) {
            String s1 = sOK.nextLine();
            String s2 = sOUT.nextLine();

            if (!s2.contains(s1)) {
                System.out.println(s2 + " " + s1);
                return "Invalid output";
            }
        }
        return "Valid output";
    }