def test_insert_at(self):
llist = SinglyLinkedList()
self.assertRaises(Exception, llist.insert_at, 1, 0)
llist.insert_at(0, 0)
self.assertEqual(llist.size, 1)
self.assertEqual(llist.head.data, 0)
llist.insert_at(0, -1)
self.assertEqual(llist.size, 2)
self.assertEqual(llist.head.data, -1)
self.assertEqual(llist.head.next.data, 0)
llist.insert_at(2, 1)
self.assertEqual(llist.size, 3)
self.assertEqual(llist.head.data, -1)
self.assertEqual(llist.head.next.data, 0)
self.assertEqual(llist.head.next.next.data, 1)
