def test_sub(self):
s1 = Stack()
s2 = Stack()
s3 = Stack()
c1 = Card(0, 0)
c2 = Card(0, 1)
c3 = Card(0, 2)
c4 = Card(0, 3)
s3 += c1
s3 += c2
s1 = s1 + c1 + c2 + c3
s2.cards = s1.cards[:]
s1 = s1 - c1
s1 = s1 - c4
self.assertFalse(c1 in s1)
self.assertEqual(len(s1), 2)
self.assertFalse(c4 in s1)
self.assertEqual(len(s2), 3)
self.assertEqual(len(s3), 2)
s2 = s2.__sub__(s3)
self.assertTrue(isinstance(s3, Stack))
self.assertEqual(len(s3), 2)
self.assertEqual(len(s2), 1)
self.assertTrue(c3 in s2)
self.assertFalse(c1 in s2)
