### Question:
StringEscapeUtil { public static String unescapeFEEL(String lexeme) { if (StringUtils.isEmpty(lexeme)) { return lexeme; } String value = stripQuotes(lexeme); StringBuilder builder = new StringBuilder(); int index = 0; while (index < value.length()) { char ch = value.charAt(index); if (ch == '\\') { if (contains(FEEL_UNESCAPE_MAP.keySet(), value, index + 1)) { builder.append(FEEL_UNESCAPE_MAP.get(value.charAt(index + 1))); index += 2; } else if (contains(REGEXP_UNESCAPE_MAP.keySet(), value, index + 1)) { builder.append(REGEXP_UNESCAPE_MAP.get(value.charAt(index + 1))); index += 2; } else if (isUnicodeEscape(value, index + 1)) { String hexCode = value.substring(index + 2, index + 6); builder.appendCodePoint(Integer.parseInt(hexCode, 16)); index += 6; } else { builder.append('\\'); index++; } } else { builder.append(ch); index++; } } return builder.toString(); }  static String stripQuotes(String value); static String unescapeFEEL(String lexeme); static String escapeFEEL(String value); static String escapeInString(String text);  }### Answer:
@Test public void testUnescapeFEEL() { assertNull(StringEscapeUtil.unescapeFEEL(null)); assertEquals("", StringEscapeUtil.unescapeFEEL("")); assertEquals("abc", StringEscapeUtil.unescapeFEEL("abc")); assertEquals("abc", StringEscapeUtil.unescapeFEEL("abc")); assertEquals("Don't consider", StringEscapeUtil.unescapeFEEL("\"Don't consider\"")); assertEquals("\n", StringEscapeUtil.unescapeFEEL("\\n")); assertEquals("\r", StringEscapeUtil.unescapeFEEL("\\r")); assertEquals("\t", StringEscapeUtil.unescapeFEEL("\\t")); assertEquals("\'", StringEscapeUtil.unescapeFEEL("\\'")); assertEquals("\"", StringEscapeUtil.unescapeFEEL("\\\"")); assertEquals("\\", StringEscapeUtil.unescapeFEEL("\\\\")); assertEquals("\\s", StringEscapeUtil.unescapeFEEL("\\s")); assertEquals("\\d", StringEscapeUtil.unescapeFEEL("\\d")); assertEquals("\t", StringEscapeUtil.unescapeFEEL("\\u0009")); assertEquals("\\u0009", StringEscapeUtil.unescapeFEEL("\\\\u0009")); assertEquals("\uD83D\uDCA9", StringEscapeUtil.unescapeFEEL("\\uD83D\\uDCA9")); assertEquals("\ud83d\udca9", StringEscapeUtil.unescapeFEEL("\\ud83d\\udca9")); assertEquals("\ud83d\udc0e\uD83D\uDE00", StringEscapeUtil.unescapeFEEL("\\ud83d\\udc0e\\uD83D\\uDE00")); assertEquals("🐎😀", StringEscapeUtil.unescapeFEEL("🐎😀")); }