      "\n",
      "class TestMergeSort(object):\n",
      "\n",
      "    def test_merge_sort(self):\n",
      "        print('None input')\n",
      "        assert_raises(TypeError, merge_sort.sort, None)\n",
      "\n",
      "        print('Empty input')\n",
      "        assert_equal(merge_sort.sort([]), [])\n",
 
</s> remove     "        data = None\n",
    "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, None)\n",
 </s> add     "        assert_raises(TypeError, merge_sort.sort, None)\n", </s> remove     "        data = None\n",
    "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, None)\n",
 </s> add     "        assert_raises(TypeError, merge_sort.sort, None)\n",
    "        merge_sort = MergeSort()\n",
    "\n",
      "\n",
      "class TestMergeSort(object):\n",
      "\n",
      "    def test_merge_sort(self):\n",
    "        merge_sort = MergeSort()\n",
    "\n",
      "        print('None input')\n",
      "        assert_raises(TypeError, merge_sort.sort, None)\n",
      "\n",
      "        print('Empty input')\n",
      "        assert_equal(merge_sort.sort([]), [])\n",
keep keep keep add keep keep keep keep keep
 Update merge sort challenge (#130)

Update constraints, test cases, code, and tests. 
sorting_searching/merge_sort/merge_sort_challenge.ipynb