### Question:
SignalUtil { public static byte[] fourBytesFromInt(int n) { ByteBuffer buff = ByteBuffer.allocate(Integer.BYTES); buff.putInt(n); return buff.array(); }  static int intFromTwoBytes(byte[] bytes); static byte[] fourBytesFromInt(int n); static byte[] twoBytesFromInt(int n); static int intFromFourBytes(byte[] bytes); static int unsign(byte by); static byte sign(int by); static byte[] joinBytesArrays(byte[]... args); static byte[] joinBytesArrays(List<byte[]> args); static int multipleOfFour(int start); static byte[] xor(byte[] a, byte[] b); static long computeCRC32(byte[] bytes); static long computeCRC32c(byte[] bytes); static byte[] flipBytes(byte[] bytes); static byte[] longToFourBytes(long l); static byte[] longToFourBytesFlip(long l); static byte[] longToBytes(long l); static byte[] padToMultipleOfFour(byte[] bytes); static long bytesToLong(byte[] l); static byte[] md5key(byte[] key); static byte[] hmacSha1(byte[] data, byte[] key); static ByteRange range(int a, int b); static byte[] copyRange(byte[] bytes,ByteRange range); static List<byte[]> split(byte[] data,int chunkSize); static byte[] randomBytes(int lgt);  }### Answer:
@Test public void fourBytesFromInt() { SignalUtil.fourBytesFromInt(0); byte[] a = {0,0,0,0}; byte[] b = {0,0,0,5}; byte[] c = {0,1,0,5}; byte[] d = {2,1,0,5}; assertTrue(Arrays.equals(a, SignalUtil.fourBytesFromInt(0))); assertTrue(Arrays.equals(b, SignalUtil.fourBytesFromInt(5))); int num = 0x00010005; byte[] ts = SignalUtil.fourBytesFromInt(num); assertTrue(Arrays.equals(c,ts)); num = 0x02010005; ts = SignalUtil.fourBytesFromInt(num); assertTrue(Arrays.equals(d,ts)); }