      }
     ],
     "source": [
      "%%writefile test_merge_sort.py\n",
      "from nose.tools import assert_equal\n",
      "\n",
      "\n",
      "class TestMergeSort(object):\n",
      "    def test_merge_sort(self):\n",
      "        print('None input')\n",
 
</s> remove     "from nose.tools import assert_equal\n",
 </s> add     "from nose.tools import assert_equal, assert_raises\n",
    "from nose.tools import assert_equal, assert_raises\n",
      }
     ],
     "source": [
      "%%writefile test_merge_sort.py\n",
    "from nose.tools import assert_equal, assert_raises\n",
      "\n",
      "\n",
      "class TestMergeSort(object):\n",
      "    def test_merge_sort(self):\n",
      "        print('None input')\n",
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