### Question:
ByteUtil { public static byte[] setBit(byte[] data, int pos, int val) { if ((data.length * 8) - 1 < pos) { throw new Error("outside byte array limit, pos: " + pos); } int posByte = data.length - 1 - (pos) / 8; int posBit = (pos) % 8; byte setter = (byte) (1 << (posBit)); byte toBeSet = data[posByte]; byte result; if (val == 1) { result = (byte) (toBeSet | setter); } else { result = (byte) (toBeSet & ~setter); } data[posByte] = result; return data; } private  ByteUtil(); static byte[] appendByte(byte[] bytes, byte b); static byte[] cloneBytes(byte[] bytes); static byte[] bigIntegerToBytes(BigInteger b, int numBytes); static byte[] bigIntegerToBytes(BigInteger value); static byte[] parseBytes(byte[] input, int offset, int len); static int matchingNibbleLength(byte[] a, byte[] b); static byte[] longToBytes(long val); static byte[] longToBytesNoLeadZeroes(long val); static byte[] intToBytes(int val); static byte[] intToBytesNoLeadZeroes(int val); static String toHexString(byte[] data); static byte[] calcPacketLength(byte[] msg); static int byteArrayToInt(byte[] b); static long byteArrayToLong(byte[] b); static String nibblesToPrettyString(byte[] nibbles); static String oneByteToHexString(byte value); static int numBytes(String val); static int firstNonZeroByte(byte[] data); static byte[] stripLeadingZeroes(byte[] data); static boolean increment(byte[] bytes); static byte[] copyToArray(BigInteger value); static ByteArrayWrapper wrap(byte[] data); static byte[] setBit(byte[] data, int pos, int val); static int getBit(byte[] data, int pos); static byte[] and(byte[] b1, byte[] b2); static byte[] or(byte[] b1, byte[] b2); static byte[] merge(byte[]... arrays); static boolean isSingleZero(byte[] array); static boolean isAllZeroes(byte[] array); static Set<T> difference(Set<T> setA, Set<T> setB); static int length(byte[]... bytes); static short bigEndianToShort(byte[] bs); static short bigEndianToShort(byte[] bs, int off); static byte[] shortToBytes(short n); static int numberOfLeadingZeros(byte[] bytes); static byte[] leftPadBytes(@Nonnull byte[] original, int newLength); static boolean fastEquals(byte[] left, byte[] right); static final byte[] EMPTY_BYTE_ARRAY; }### Answer:
@Test public void setBitTest() { byte[] data = ByteBuffer.allocate(4).putInt(0).array(); int posBit = 24; int expected = 16777216; int result = -1; byte[] ret = ByteUtil.setBit(data, posBit, 1); result = ByteUtil.byteArrayToInt(ret); assertTrue(expected == result); posBit = 25; expected = 50331648; ret = ByteUtil.setBit(data, posBit, 1); result = ByteUtil.byteArrayToInt(ret); assertTrue(expected == result); posBit = 2; expected = 50331652; ret = ByteUtil.setBit(data, posBit, 1); result = ByteUtil.byteArrayToInt(ret); assertTrue(expected == result); posBit = 24; expected = 33554436; ret = ByteUtil.setBit(data, posBit, 0); result = ByteUtil.byteArrayToInt(ret); assertTrue(expected == result); posBit = 25; expected = 4; ret = ByteUtil.setBit(data, posBit, 0); result = ByteUtil.byteArrayToInt(ret); assertTrue(expected == result); posBit = 2; expected = 0; ret = ByteUtil.setBit(data, posBit, 0); result = ByteUtil.byteArrayToInt(ret); assertTrue(expected == result); }