def test_insertAfter_middleDouble():
  test_list = LinkedList()
  test_list.insert(2)
  test_list.insert(2)
  test_list.insert(1)
  test_list.insertAfter(2,5)
  actual = str(test_list)
  expected = "{ 1 } -> { 2 } -> { 5 } -> { 2 } -> NULL"
  assert actual == expected
def test_insertAfter_notInList():
  test_list = LinkedList()
  test_list.insert(2)
  test_list.insert(3)
  test_list.insert(1)
  actual = test_list.insertAfter(4,5)
  expected = "An error has occured"
  assert actual == expected