@Test
 public void testHasPrevious() {
   assertFalse(Ipv4.FIRST_IPV4_ADDRESS.hasPrevious());
   assertTrue(Ipv4.of("192.168.0.1").hasPrevious());
   assertTrue(Ipv4.LAST_IPV4_ADDRESS.hasPrevious());
 }
 @Test
 public void shouldHave32BitsSize() {
   assertEquals(Ipv4.NUMBER_OF_BITS, Ipv4.FIRST_IPV4_ADDRESS.bitSize());
 }