     "metadata": {},
     "source": [
      "## Test Cases\n",
      "\n",
      "* None -> None\n",
      "* Empty input -> []\n",
      "* One element -> [element]\n",
      "* Two or more elements\n",
      "* Left and right subarrays of different lengths"
     ]
 
</s>
    "* None -> Exception\n",
     "metadata": {},
     "source": [
      "## Test Cases\n",
      "\n",
    "* None -> Exception\n",
      "* Empty input -> []\n",
      "* One element -> [element]\n",
      "* Two or more elements\n",
      "* Left and right subarrays of different lengths"
     ]
keep keep keep keep replace keep keep keep keep keep
 Update merge sort challenge (#130)

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