### Question:
Numeric { public static String cleanHexPrefix(String input) { if (containsHexPrefix(input)) { return input.substring(2); } else { return input; } } private  Numeric(); static String encodeQuantity(BigInteger value); static BigInteger decodeQuantity(String value); static String cleanHexPrefix(String input); static String prependHexPrefix(String input); static boolean containsHexPrefix(String input); static BigInteger toBigInt(byte[] value, int offset, int length); static BigInteger toBigInt(byte[] value); static BigInteger toBigInt(String hexValue); static BigInteger toBigIntNoPrefix(String hexValue); static String toHexStringWithPrefix(BigInteger value); static String toHexStringNoPrefix(BigInteger value); static String toHexStringNoPrefix(byte[] input); static String toHexStringWithPrefixZeroPadded(BigInteger value, int size); static String toHexStringNoPrefixZeroPadded(BigInteger value, int size); static byte[] toBytesPadded(BigInteger value, int length); static byte[] hexStringToByteArray(String input); static String toHexString(byte[] input, int offset, int length, boolean withPrefix); static String toHexString(byte[] input); static byte asByte(int m, int n); static boolean isIntegerValue(BigDecimal value);  }### Answer:
@Test public void testCleanHexPrefix() { assertThat(Numeric.cleanHexPrefix(""), is("")); assertThat(Numeric.cleanHexPrefix("0123456789abcdef"), is("0123456789abcdef")); assertThat(Numeric.cleanHexPrefix("0x"), is("")); assertThat(Numeric.cleanHexPrefix("0x0123456789abcdef"), is("0123456789abcdef")); }