docs: public static String getPlatform(RemoteProxy proxy) {
      if (proxy.getTestSlots().size() == 0) {
        return "Unknown";
      }
      Platform res = getPlatform(proxy.getTestSlots().get(0));
  
      for (TestSlot slot : proxy.getTestSlots()) {
        Platform tmp = getPlatform(slot);
        if (tmp != res) {
          return "mixed OS";
        }
        res = tmp;
      }
      if (res == null) {
        return "not specified";
      }
      return res.toString();
    }