private static void check (String plainText, String base64Text) 
{
   String s1 = Base64Coder.encodeString(plainText);
   String s2 = Base64Coder.decodeString(base64Text);
   if (!s1.equals(base64Text) || !s2.equals(plainText))
      fail ("Check failed for \""+plainText+"\" / \""+base64Text+"\"."); 
}