### Question:
Utils { public static boolean isDecimalString(String s) { return s.matches("^\\d+$"); }  static BigInteger unifiedNumericToBigInteger(String number); static String longToDateTime(long timestamp); static String getValueShortString(BigInteger number); static byte[] addressStringToBytes(String hex); static boolean isValidAddress(byte[] addr); static String getAddressShortString(byte[] addr); static SecureRandom getRandom(); static String getHashListShort(List<byte[]> blockHashes); static String getNodeIdShort(String nodeId); static long toUnixTime(long javaTime); static long fromUnixTime(long unixTime); static T[] mergeArrays(T[] ... arr); static String align(String s, char fillChar, int targetLen, boolean alignRight); static String repeat(String s, int n); static boolean contains(List<byte[]> list, byte[] valueToFind); static void validateArrayAllegedSize(byte[] data, int offset, int allegedSize); static byte[] safeCopyOfRange(byte[] data, int from, int size); static boolean isDecimalString(String s); static boolean isHexadecimalString(String s); static long decimalStringToLong(String s); static long hexadecimalStringToLong(String s); static final double JAVA_VERSION; }### Answer:
@Test public void isDecimalString() { String[] decStrings = new String[] { "1", "123", "045670", "220", "0", "01" }; java.util.Arrays.stream(decStrings).forEach(s -> Assert.assertTrue(s, Utils.isDecimalString(s))); String[] nonDecStrings = new String[] { "hellothisisnotadec", "123a", "0b", "b1", "AAA", "0xabcd", "0x123" }; java.util.Arrays.stream(nonDecStrings).forEach(s -> Assert.assertFalse(s, Utils.isDecimalString(s))); }