code: public static String getQuotedString(String st) {
      Preconditions.checkNotNull(st);
      String quotedString = "";
      if (!st.startsWith(SINGLE_QUOTE)) {
        quotedString += SINGLE_QUOTE;
      }
      quotedString += st;
      if (!st.endsWith(SINGLE_QUOTE)) {
        quotedString += SINGLE_QUOTE;
      }
      return quotedString;
    }
docs: Add single quotes to the string, if not present.
  TestString will be converted to 'TestString'