### Question:
HexUtil { public static byte toByteFromHex(char upperChar, char lowerChar) { byte upper = HEX_TO_BYTE_MAP.get(Character.toLowerCase(upperChar)); byte lower = HEX_TO_BYTE_MAP.get(Character.toLowerCase(lowerChar)); return (byte) ((upper << BITS_PER_HEX_DIGIT) + lower); }  static String toHexFromByte(final byte b); static byte toByteFromHex(char upperChar, char lowerChar); static String toHexFromBytes(final ByteBuffer bytes); static String toHexFromBytes(final byte[] bytes); static byte[] toBytesFromHex(String hexStr); final static int BITS_PER_HEX_DIGIT; }### Answer:
@Test public void testByteToHex() { Assert.assertEquals((byte)0x00, HexUtil.toByteFromHex('0','0')); Assert.assertEquals((byte)0x01, HexUtil.toByteFromHex('0','1')); Assert.assertEquals((byte)0x02, HexUtil.toByteFromHex('0','2')); Assert.assertEquals((byte)0x03, HexUtil.toByteFromHex('0','3')); Assert.assertEquals((byte)0x04, HexUtil.toByteFromHex('0','4')); Assert.assertEquals((byte)0x05, HexUtil.toByteFromHex('0','5')); Assert.assertEquals((byte)0x06, HexUtil.toByteFromHex('0','6')); Assert.assertEquals((byte)0x07, HexUtil.toByteFromHex('0','7')); Assert.assertEquals((byte)0x08, HexUtil.toByteFromHex('0','8')); Assert.assertEquals((byte)0x09, HexUtil.toByteFromHex('0','9')); Assert.assertEquals((byte)0x0a, HexUtil.toByteFromHex('0','a')); Assert.assertEquals((byte)0x0b, HexUtil.toByteFromHex('0','b')); Assert.assertEquals((byte)0x0c, HexUtil.toByteFromHex('0','c')); Assert.assertEquals((byte)0x0d, HexUtil.toByteFromHex('0','d')); Assert.assertEquals((byte)0x0e, HexUtil.toByteFromHex('0','e')); Assert.assertEquals((byte)0x0f, HexUtil.toByteFromHex('0','f')); Assert.assertEquals((byte)0x23, HexUtil.toByteFromHex('2','3')); Assert.assertEquals((byte)0x19, HexUtil.toByteFromHex('1','9')); Assert.assertEquals((byte)0x75, HexUtil.toByteFromHex('7','5')); Assert.assertEquals((byte)0x43, HexUtil.toByteFromHex('4','3')); Assert.assertEquals((byte)0xa9, HexUtil.toByteFromHex('a','9')); Assert.assertEquals((byte)0x3b, HexUtil.toByteFromHex('3','b')); Assert.assertEquals((byte)0xc3, HexUtil.toByteFromHex('c','3')); Assert.assertEquals((byte)0xff, HexUtil.toByteFromHex('f','f')); }