      "        sorted_data = merge_sort(data)\n",
      "        assert_equal(sorted_data, [])\n",
      "\n",
      "        print('One element')\n",
      "        data = [5]\n",
      "        sorted_data = merge_sort(data)\n",
      "        assert_equal(sorted_data, [5])\n",
      "\n",
      "        print('Two or more elements')\n",
      "        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]\n",
      "        sorted_data = merge_sort(data)\n",
      "        assert_equal(sorted_data, sorted(data))\n",
 
</s> remove     "        data = [5]\n",
    "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, [5])\n",
 </s> add     "        assert_equal(merge_sort.sort([5]), [5])\n", </s> remove     "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, sorted(data))\n",
 </s> add     "        assert_equal(merge_sort.sort(data), sorted(data))\n", </s> remove     "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, sorted(data))\n",
 </s> add     "        assert_equal(merge_sort.sort(data), sorted(data))\n", </s> remove     "        data = []\n",
    "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, [])\n",
 </s> add     "        assert_equal(merge_sort.sort([]), [])\n", </s> remove     "        data = []\n",
    "        sorted_data = merge_sort(data)\n",
    "        assert_equal(sorted_data, [])\n",
 </s> add     "        assert_equal(merge_sort.sort([]), [])\n",
    "        assert_equal(merge_sort.sort([5]), [5])\n",
      "        sorted_data = merge_sort(data)\n",
      "        assert_equal(sorted_data, [])\n",
      "\n",
      "        print('One element')\n",
    "        assert_equal(merge_sort.sort([5]), [5])\n",
    "        assert_equal(merge_sort.sort([5]), [5])\n",
    "        assert_equal(merge_sort.sort([5]), [5])\n",
      "\n",
      "        print('Two or more elements')\n",
      "        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]\n",
      "        sorted_data = merge_sort(data)\n",
      "        assert_equal(sorted_data, sorted(data))\n",
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/merge_sort_challenge.ipynb