  
  class TestMergeSort(object):
      def test_merge_sort(self):
          print('None input')
          data = None
          sorted_data = merge_sort(data)
          assert_equal(sorted_data, None)
  
          print('Empty input')
          data = []
          sorted_data = merge_sort(data)
          assert_equal(sorted_data, [])
 
</s> remove         data = []
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, [])
 </s> add         assert_equal(merge_sort.sort([]), []) </s> remove         data = [5]
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, [5])
 </s> add         assert_equal(merge_sort.sort([5]), [5]) </s> remove from nose.tools import assert_equal
 </s> add from nose.tools import assert_equal, assert_raises </s> remove         sorted_data = merge_sort(data)
        assert_equal(sorted_data, sorted(data))
 </s> add         assert_equal(merge_sort.sort(data), sorted(data))
        assert_raises(TypeError, merge_sort.sort, None)
  
  class TestMergeSort(object):
      def test_merge_sort(self):
          print('None input')
        assert_raises(TypeError, merge_sort.sort, None)
        assert_raises(TypeError, merge_sort.sort, None)
        assert_raises(TypeError, merge_sort.sort, None)
  
          print('Empty input')
          data = []
          sorted_data = merge_sort(data)
          assert_equal(sorted_data, [])
keep keep keep keep replace replace replace keep keep keep keep keep
 Update merge sort challenge (#130)

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