def test_insert(self):
"""
Tests the insert(index, data) method
"""
dll = DoublyLinkedList()
# test out of bounds
self.assertIsNone(dll.insert(-1, 'data'))
self.assertIsNone(dll.insert(1, 'data'))
# test inserting at index zero in open list (should use unshift(data))
dll.insert(0, 'node zero')
self.assertEqual(dll.length, 1)
self.assertEqual(dll.head.data, 'node zero')
dll.clear()
dll.push(0) # index 0
dll.push(1) # index 1
dll.push(2) # index 2
# insert at index 1
expected_list = [0, 'insert one', 1, 2]
self.assertIsInstance(dll.insert(1, 'insert one'), DoublyLinkedList)
self.assertEqual(dll.length, 4)
self.assertEqual(dll.to_list(), expected_list)
# insert at tail, index 4
expected_list = [0, 'insert one', 1, 2, 'insert tail']
self.assertIsInstance(dll.insert(4, 'insert tail'), DoublyLinkedList)
self.assertEqual(dll.length, 5)
self.assertEqual(dll.to_list(), expected_list)
def test_clear(self):
"""
Tests the clear() method
"""
dll = DoublyLinkedList()
dll.push('node one')
dll.push('node two')
dll.push('node three')
self.assertEqual(dll.length, 3)
self.assertIsInstance(dll.clear(), DoublyLinkedList)
self.assertEqual(dll.length, 0)
self.assertIsNone(dll.head)
self.assertIsNone(dll.tail)
