def test_shift_empty(self):
test_list = DoubleLinkedList()
self.assertEqual(test_list.shift(), "list is empty")
def test_shift(self):
test_list = DoubleLinkedList()
for i in range(5):
test_list.push(i)
for i in range(5):
self.assertEqual(test_list.shift(), i)
def test_unshift_shift(self):
test_list = DoubleLinkedList()
test_list.unshift(5)
self.assertEqual(test_list.len(), 1)
self.assertEqual(test_list.shift(), 5)