assertEquals(
        "a&quot;b&lt;c&gt;d&amp;e&quot;f&apos;", xmlAttributeEscaper.escape("a\"b<c>d&e\"f'"));
    // Test '\t', '\n' and '\r' are escaped.
    assertEquals("a&#x9;b&#xA;c&#xD;d", xmlAttributeEscaper.escape("a\tb\nc\rd"));
  }

  // Helper to assert common properties of xml escapers.
  static void assertBasicXmlEscaper(
      CharEscaper xmlEscaper, boolean shouldEscapeQuotes, boolean shouldEscapeWhitespaceChars) {