char[] surrogates = {
      MAX_LOW_SURROGATE, MAX_HIGH_SURROGATE, MIN_LOW_SURROGATE, MIN_HIGH_SURROGATE,
    };
    for (char surrogate : surrogates) {
      builder.add(newString(surrogate));
      builder.add(newString(surrogate, 'n'));
      builder.add(newString('n', surrogate));
      builder.add(newString(surrogate, surrogate));
    }

    char[] surrogates = {
      MAX_LOW_SURROGATE, MAX_HIGH_SURROGATE, MIN_LOW_SURROGATE, MIN_HIGH_SURROGATE,
    };
    for (char surrogate : surrogates) {
      builder.add(newString(surrogate));
      builder.add(newString(surrogate, 'n'));
      builder.add(newString('n', surrogate));
      builder.add(newString(surrogate, surrogate));
    }

      if (c < 0x800) {
        utf8Length += (0x7f - c) >>> 31; // branch free!
      } else {
        utf8Length += 2;
        // jdk7+: if (Character.isSurrogate(c)) {
        if (MIN_SURROGATE <= c && c <= MAX_SURROGATE) {
          // Check that we have a well-formed surrogate pair.
          if (Character.codePointAt(sequence, i) == c) {
            throw new IllegalArgumentException(unpairedSurrogateMsg(i));
          }
          i++;

      if (c < 0x800) {
        utf8Length += (0x7f - c) >>> 31; // branch free!
      } else {
        utf8Length += 2;
        // jdk7+: if (Character.isSurrogate(c)) {
        if (MIN_SURROGATE <= c && c <= MAX_SURROGATE) {
          // Check that we have a well-formed surrogate pair.
          if (Character.codePointAt(sequence, i) == c) {
            throw new IllegalArgumentException(unpairedSurrogateMsg(i));
          }
          i++;

  private static final String SMALLEST_SURROGATE =
      "" + Character.MIN_HIGH_SURROGATE + Character.MIN_LOW_SURROGATE;
  private static final String LARGEST_SURROGATE =
      "" + Character.MAX_HIGH_SURROGATE + Character.MAX_LOW_SURROGATE;

  private static final String TEST_STRING =
      "\0abyz\u0080\u0100\u0800\u1000ABYZ\uffff" + SMALLEST_SURROGATE + "0189" + LARGEST_SURROGATE;

  // Escapes nothing

  private static final String SMALLEST_SURROGATE =
      "" + Character.MIN_HIGH_SURROGATE + Character.MIN_LOW_SURROGATE;
  private static final String LARGEST_SURROGATE =
      "" + Character.MAX_HIGH_SURROGATE + Character.MAX_LOW_SURROGATE;

  private static final String TEST_STRING =
      "\0abyz\u0080\u0100\u0800\u1000ABYZ\uffff" + SMALLEST_SURROGATE + "0189" + LARGEST_SURROGATE;

  // Escapes nothing

   *             surrogate is returned.</b>
   *         <li><b>If the next character was a valid low surrogate, the code point value of the
   *             high/low surrogate pair is returned.</b>
   *         <li>If the next character was not a low surrogate value, then {@link
   *             IllegalArgumentException} is thrown.
   *       </ol>

 * because of the possibility of splitting a surrogate pair. The only case in which it is safe to
 * escape strings and concatenate the results is if you can rule out this possibility, either by
 * splitting an existing long string into short strings adaptively around {@linkplain
 * Character#isHighSurrogate surrogate} {@linkplain Character#isLowSurrogate pairs}, or by starting

        do {
          codePoints[i] = rng.nextInt(0x800);
        } while (!Character.isValidCodePoint(codePoints[i])
            || (codePoints[i] >= Character.MIN_SURROGATE
                && codePoints[i] <= Character.MAX_SURROGATE));
      }
      StringBuilder builder = new StringBuilder();
      for (int i = 0; i < codePoints.length; i++) {
        builder.appendCodePoint(codePoints[i]);
      }

    assertEquals("abc", Strings.commonPrefix(new StringBuffer("abcdef"), "abcxyz"));

    // Identical valid surrogate pairs.
    assertEquals(
        "abc\uD8AB\uDCAB", Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCABxyz"));
    // Differing valid surrogate pairs.
    assertEquals("abc", Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCACxyz"));
    // One invalid pair.