### Question:
Str extends RapidoidThing { public static String camelToSnake(String s) { return U.join("_", Str.camelSplit(s)).toLowerCase(); } private  Str(); static String[] camelSplit(String s); static String phrase(String s); static String replace(String s, String[][] repls); static String mask(String target, Pattern regex); static int find(String target, String regex, final Operation<String[]> action); static String replace(String target, String regex, Mapper<String[], String> replacer); static String replace(String target, Pattern regex, Mapper<String[], String> replacer); static String replace(String target, String mask, Pattern regex, Mapper<String[], String> replacer); static String render(Object[] items, String itemFormat, String sep); static String render(Iterable<?> items, String itemFormat, String sep); static String render(Map<?, ?> items, String itemFormat, String sep); static String capitalized(String s); static String uncapitalized(String s); static String mul(String s, int n); static String sub(String s, int beginIndex, int endIndex); static String trimr(String s, char suffix); static String trimr(String s, String suffix); static String triml(String s, char prefix); static String triml(String s, String prefix); static String insert(String target, int atIndex, String insertion); static String cutToFirst(String s, String delimiter); static String cutToLast(String s, String delimiter); static String cutFromFirst(String s, String delimiter); static String cutFromLast(String s, String delimiter); static String xmlEscape(String s); static String javaEscape(String s); static String camelToSnake(String s); static String toHex(byte[] data); static byte[] fromHex(String hex); static String toBase64(byte[] data); static String toBase64(byte[] data, char plusReplacement, char slashReplacement); static String toWebSafeBase64(byte[] data); static String toWebSafeBinary(byte[] data); static boolean isWebSafeBinary(String s); static byte[] fromWebSafeBinary(String binary); static byte[] fromBase64(String base64); static byte[] fromBase64(String base64, char plusReplacement, char slashReplacement); static byte[] fromWebSafeBase64(String base64); static String wildcardToRegex(String pattern); static String wildcardsToRegex(String... patterns); static List<String> linesOf(String s); static List<String> grep(String regex, Iterable<String> lines); static String textToId(String s); static final String CAMEL_REGEX; }### Answer:
@Test public void testCamelToSnake() { eq(Str.camelToSnake("bookTitle"), "book_title"); eq(Str.camelToSnake("BookTitle"), "book_title"); eq(Str.camelToSnake("Foo"), "foo"); eq(Str.camelToSnake("bar"), "bar"); eq(Str.camelToSnake("ABC"), "abc"); eq(Str.camelToSnake("myID"), "my_id"); eq(Str.camelToSnake("xID2"), "x_id_2"); eq(Str.camelToSnake("date1"), "date_1"); eq(Str.camelToSnake("myDate2"), "my_date_2"); }