### Question:
NumberUtil { public static String toString(int i) { return Integer.toString(i); }  static boolean equalsWithin(double d1, double d2); static boolean equalsWithin(double d1, double d2, double epsilon); static byte[] toBytes(int value); static byte[] toBytes(long value); static byte[] toBytes(double val); static int toInt(byte[] bytes); static long toLong(byte[] bytes); static double toDouble(byte[] bytes); static boolean isNumber(@Nullable String str); static boolean isHexNumber(@Nullable String value); static int toInt(@NotNull String str); static int toInt(@Nullable String str, int defaultValue); static long toLong(@NotNull String str); static long toLong(@Nullable String str, long defaultValue); static double toDouble(@NotNull String str); static double toDouble(@Nullable String str, double defaultValue); static Integer toIntObject(@NotNull String str); static Integer toIntObject(@Nullable String str, Integer defaultValue); static Long toLongObject(@NotNull String str); static Long toLongObject(@Nullable String str, Long defaultValue); static Double toDoubleObject(@NotNull String str); static Double toDoubleObject(@Nullable String str, Double defaultValue); static Integer hexToIntObject(@NotNull String str); static Integer hexToIntObject(@Nullable String str, Integer defaultValue); static Long hexToLongObject(@NotNull String str); static Long hexToLongObject(@Nullable String str, Long defaultValue); static String toString(int i); static String toString(@NotNull Integer i); static String toString(long l); static String toString(@NotNull Long l); static String toString(double d); static String toString(@NotNull Double d); static String to2DigitString(double d); static int toInt32(long x);  }### Answer:
@Test public void toStringTest() { assertThat(NumberUtil.toString(23)).isEqualTo("23"); assertThat(NumberUtil.toString(new Integer(23))).isEqualTo("23"); assertThat(NumberUtil.toString(23l)).isEqualTo("23"); assertThat(NumberUtil.toString(new Long(23))).isEqualTo("23"); assertThat(NumberUtil.toString(23l)).isEqualTo("23"); assertThat(NumberUtil.toString(new Double(23.112d))).isEqualTo("23.112"); assertThat(NumberUtil.toString(23.112d)).isEqualTo("23.112"); assertThat(NumberUtil.to2DigitString(23.112d)).isEqualTo("23.11"); assertThat(NumberUtil.to2DigitString(23.116d)).isEqualTo("23.12"); }