text: from challenges.merge_sort.merge_sort import merge_sort
  
  def test_normal_merge_sort():
      arr = [1,3,2,5,4]
      merge_sort(arr)
      actual = arr
      expected = [1,2,3,4,5]
      assert actual == expected
  
  def test_one_index_merge_sort():
      arr = [1]
      merge_sort(arr)
      actual = arr
      expected = [1]
      assert actual == expected
  
  def test_no_index_merge_sort():
      arr = []
      merge_sort(arr)
      actual = arr
      expected = []
      assert actual == expected
  
  def test_repeat_index_merge_sort():
      arr = [2,2,2,2,1]
      merge_sort(arr)
      actual = arr
      expected = [1,2,2,2,2]
      assert actual == expected
  
  def test_negative_number_merge_sort():
      arr = [-1,-2,-3,-4,-5]
      merge_sort(arr)
      actual = arr
      expected = [-5,-4,-3,-2,-1]
      assert actual == expected
  