def test_string_keys(self):
p = Preferences(('A', 'B'))
self.assertTrue(p.prefers('A', 'B'))
self.assertFalse(p.prefers('B', 'A'))
self.assertEqual({'A'}, set(p.all_preferred_to('B')))
def test_all_preferred_to(self):
p = Preferences([1, 2, 3, 4, 5])
self.assertEqual({1, 2, 3}, set(p.all_preferred_to(4)))
self.assertEqual({1, 2, 3, 4}, set(p.all_preferred_to(5)))
self.assertEqual(set(), set(p.all_preferred_to(1)))
self.assertEqual(set(), set(p.all_preferred_to(6)))
