### Question:
ByteUtilities { static byte[] concat(byte[] b1, byte[] b2, int b2Length) { byte[] concat = new byte[b1.length + b2Length]; System.arraycopy(b1, 0, concat, 0, b1.length); System.arraycopy(b2, 0, concat, b1.length, b2Length); return concat; } private  ByteUtilities(); static int readNBytes(InputStream in, OutputStream out, int byteCount); static boolean readUntilInclusive(PushbackInputStream in, OutputStream out, byte[] marker);  }### Answer:
@Test public void testConcat() { Assert.assertTrue(Arrays.equals(new byte[] { 1, 2, 3, 4, 5, 6 }, ByteUtilities.concat(new byte[] { 1, 2 }, new byte[] { 3, 4, 5, 6 }, 4))); }