  class TestMergeSort(object):
  
      def test_merge_sort(self):
          print('None input')
          assert_raises(TypeError, merge_sort.sort, None)
  
          print('Empty input')
 
</s> remove         data = None
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, None)
 </s> add         assert_raises(TypeError, merge_sort.sort, None) </s> remove from nose.tools import assert_equal
 </s> add from nose.tools import assert_equal, assert_raises </s> remove         data = []
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, [])
 </s> add         assert_equal(merge_sort.sort([]), [])
        merge_sort = MergeSort()

  class TestMergeSort(object):
  
      def test_merge_sort(self):
        merge_sort = MergeSort()

          print('None input')
          assert_raises(TypeError, merge_sort.sort, None)
  
          print('Empty input')
keep keep add keep keep keep keep
 Update merge sort challenge (#130)

Update constraints, test cases, code, and tests. 
sorting_searching/merge_sort/test_merge_sort.py