### Question:
StringEscapeUtil { public static String escapeFEEL(String value) { if (StringUtils.isEmpty(value)) { return value; } StringBuilder builder = new StringBuilder(); int index = 0; while (index < value.length()) { char ch = value.charAt(index); if (ch == '\\') { if (contains(REGEXP_ESCAPE_MAP.keySet(), value, index + 1)) { builder.append(REGEXP_ESCAPE_MAP.get(value.charAt(index + 1))); index += 2; } else { builder.append('\\'); builder.append('\\'); index++; } } else if (FEEL_ESCAPE_MAP.containsKey(ch)) { builder.append(FEEL_ESCAPE_MAP.get(ch)); index++; } else if (Character.isSurrogate(ch)) { builder.append("\\u").append(hex(ch)); 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 testEscapeFEEL() { assertNull(StringEscapeUtil.escapeFEEL(null)); assertEquals("", StringEscapeUtil.escapeFEEL("")); assertEquals("abc", StringEscapeUtil.escapeFEEL("abc")); assertEquals("Don't consider", StringEscapeUtil.escapeFEEL("Don't consider")); assertEquals("\\n", StringEscapeUtil.escapeFEEL("\n")); assertEquals("\\r", StringEscapeUtil.escapeFEEL("\r")); assertEquals("\\t", StringEscapeUtil.escapeFEEL("\t")); assertEquals("'", StringEscapeUtil.escapeFEEL("\'")); assertEquals("\\\"", StringEscapeUtil.escapeFEEL("\"")); assertEquals("\\\\", StringEscapeUtil.escapeFEEL("\\")); assertEquals("\\\\s", StringEscapeUtil.escapeFEEL("\\s")); assertEquals("\\\\d", StringEscapeUtil.escapeFEEL("\\d")); assertEquals("\\t", StringEscapeUtil.escapeFEEL("\u0009")); assertEquals("\\\\u0009", StringEscapeUtil.escapeFEEL("\\u0009")); assertEquals("\\uD83D\\uDCA9", StringEscapeUtil.escapeFEEL("\uD83D\uDCA9")); assertEquals("\\uD83D\\uDCA9", StringEscapeUtil.escapeFEEL("\ud83d\udca9")); assertEquals("\\uD83D\\uDC0E\\uD83D\\uDE00", StringEscapeUtil.escapeFEEL("\ud83d\udc0e\uD83D\uDE00")); assertEquals("\\uD83D\\uDC0E\\uD83D\\uDE00", StringEscapeUtil.escapeFEEL("🐎😀")); }