def test_year(self):
        cases = [(2000, "이천년"), (2002, "이천이년"), (2018, "이천십팔년"),
                 (1954, "천구백오십사년"), (1910, "천구백십년"), (-1000, "기원전 천년")]
        for num, out in cases:
            self.assertEqual(n2k(num, to="year"), out)