def test_get_next_sibling_4(self):
     identifier = SystematicIdentifier("1.1.7", 5, 3)
     self.assertEqual(identifier.get_next_sibling_identifier(),
                      SystematicIdentifier("1.1.7", 5, 4))
 def test_get_next_sibling_1(self):
     identifier = SystematicIdentifier("1")
     self.assertEqual(identifier.get_next_sibling_identifier(),
                      SystematicIdentifier("2"))