@Test
 public void testWhenValidPinNumber() throws Exception {
   Assert.assertTrue(validator.isValid(1, null));
 }
 @Test
 public void testWhenNull() throws Exception {
   Assert.assertFalse(validator.isValid(null, null));
 }
 @Test
 public void testWhenInvalidPinNumber() throws Exception {
   Assert.assertFalse(validator.isValid(50, null));
 }