sb.setLength(0);
      int utf8Length = 0;
      for (int i = 0; i < 6; i++) {
        Integer randomCodePoint = codePoints[rnd.nextInt(codePoints.length)];
        sb.appendCodePoint(randomCodePoint);
        utf8Length += requireNonNull(utf8Lengths.get(randomCodePoint));
        if (utf8Length != Utf8.encodedLength(sb)) {
          StringBuilder repro = new StringBuilder();