}

  /**
   * Asserts that a Unicode escaper escapes the given hi/lo surrogate pair into the expected string.
   *
   * @param escaper the non-null escaper to test
   * @param expected the expected output string
   * @param hi the high surrogate pair character
   * @param lo the low surrogate pair character
   */
  public static void assertUnicodeEscaping(

  }

  /**
   * Asserts that a Unicode escaper escapes the given hi/lo surrogate pair into the expected string.
   *
   * @param escaper the non-null escaper to test
   * @param expected the expected output string
   * @param hi the high surrogate pair character
   * @param lo the low surrogate pair character
   */
  public static void assertUnicodeEscaping(

        };
    EscaperAsserts.assertBasic(surrogateEscaper);

    // A surrogate pair defining a code point within the safe range.
    String safeInput = "\uD800\uDC00"; // 0x10000
    assertThat(surrogateEscaper.escape(safeInput)).isEqualTo(safeInput);

    // A surrogate pair defining a code point outside the safe range (but both
    // of the surrogate characters lie within the safe range). It is important

    // Build up a range of surrogate pair characters to test
    int min = Character.MIN_SUPPLEMENTARY_CODE_POINT;
    int max = Character.MAX_CODE_POINT;
    int range = max - min;
    int s1 = min + (1 * range) / 4;
    int s2 = min + (2 * range) / 4;
    int s3 = min + (3 * range) / 4;
    char[] dst = new char[12];

    // Put surrogate pairs at odd indices so they can be split easily

    assertThat(Strings.commonPrefix(new StringBuilder("abcdef"), "abcxyz")).isEqualTo("abc");

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

    assertStringHash(0xb5a4be05, "ABCDefGHI\u0799", UTF_8);
    assertStringHash(0xfc5ba834, "毎月１日,毎週月曜日", UTF_8);
    assertStringHash(0x8a5c3699, "surrogate pair: \uD83D\uDCB0", UTF_8);

    assertStringHash(0, "", UTF_16LE);
    assertStringHash(0x288418e4, "k", UTF_16LE);
    assertStringHash(0x5a0cb7c3, "hell", UTF_16LE);
    assertStringHash(0xd7c31989, "hello", UTF_16LE);

   * Specifically "\r" (carriage return) is preserved in the output, which may result in it being
   * silently converted to "\n" when the XML is parsed.
   *
   * <p>This escaper does not treat surrogate pairs specially and does not perform Unicode
   * validation on its input.
   */
  public static Escaper xmlContentEscaper() {
    return XML_CONTENT_ESCAPER;
  }

  /**

    return new String(array);
  }

  /**
   * Returns the longest string {@code prefix} such that {@code a.toString().startsWith(prefix) &&
   * b.toString().startsWith(prefix)}, taking care not to split surrogate pairs. If {@code a} and
   * {@code b} have no common prefix, returns the empty string.
   *
   * @since 11.0
   */
  public static String commonPrefix(CharSequence a, CharSequence b) {
    checkNotNull(a);

    assertStringHash(0xb5a4be05, "ABCDefGHI\u0799", UTF_8);
    assertStringHash(0xfc5ba834, "毎月１日,毎週月曜日", UTF_8);
    assertStringHash(0x8a5c3699, "surrogate pair: \uD83D\uDCB0", UTF_8);

    assertStringHash(0, "", UTF_16LE);
    assertStringHash(0x288418e4, "k", UTF_16LE);
    assertStringHash(0x5a0cb7c3, "hell", UTF_16LE);
    assertStringHash(0xd7c31989, "hello", UTF_16LE);

        }
      } else {
        // and everything else is replaced with FFFD.
        assertEscaping(xmlEscaper, "\uFFFD", ch);
      }
    }

    // Test _all_ allowed characters (including surrogate values).
    for (char ch = 0x20; ch <= 0xFFFD; ch++) {
      // There are a small number of cases to consider, so just do it manually.
      if (ch == '&') {
        assertEscaping(xmlEscaper, "&amp;", ch);