def test_equals(self):
     self.assertEqual(next_bigger(12), 21)
 def test_equals_2(self):
     self.assertEqual(next_bigger(513), 531)
 def test_equals_7(self):
     self.assertEqual(next_bigger(1234567890), 1234567908)
 def test_equals_6(self):
     self.assertEqual(next_bigger(531), -1)
 def test_equals_5(self):
     self.assertEqual(next_bigger(111), -1)
 def test_equals_4(self):
     self.assertEqual(next_bigger(9), -1)
 def test_equals_3(self):
     self.assertEqual(next_bigger(2017), 2071)