text: from merge_sort import merge_sort
  
  
  def test_randomly_unsorted_list():
      """An unsorted list returns sorted."""
      lst = ['C', 'B', 'D', 'E', 'A']
  
      expected = ['A', 'B', 'C', 'D', 'E']
      actual = merge_sort(lst)
      assert actual == expected
  
  
  def test_sorted_list():
      """A sorted list will return unchanged."""
      lst = ['A', 'B', 'C', 'D', 'E']
  
      expected = ['A', 'B', 'C', 'D', 'E']
      actual = merge_sort(lst)
      assert actual == expected
  
  
  def test_backward_list():
      """A backward list will return reversed."""
      lst = ['E', 'D', 'C', 'B', 'A']
  
      expected = ['A', 'B', 'C', 'D', 'E']
      actual = merge_sort(lst)
      assert actual == expected
  
  
  def test_empty_list():
      """An empty list will return unchanged."""
      lst = []
  
      expected = []
      actual = merge_sort(lst)
      assert actual == expected
  
  
  def test_single_item_list():
      """A one-itemed list will return unchanged."""
      lst = ['A']
  
      expected = ['A']
      actual = merge_sort(lst)
      assert actual == expected
  