     ],
     "source": [
      "%%writefile test_check_balance.py\n",
      "from nose.tools import assert_equal\n",
      "\n",
      "\n",
      "class TestCheckBalance(object):\n",
      "\n",
      "    @raises(Exception)\n",
 
</s> remove     "    def test_check_balance(self):\n",
    "        assert_equal(check_balance(None), False)\n",
 </s> add     "    @raises(Exception)\n",
    "    def test_check_balance_empty(self):\n",
    "        check_balance(None)\n", </s> remove     "    def test_check_balance(self):\n",
    "        assert_equal(check_balance(None), False)\n",
 </s> add     "    @raises(Exception)\n",
    "    def test_check_balance_empty(self):\n",
    "        check_balance(None)\n",
    "from nose.tools import raises\n",
     ],
     "source": [
      "%%writefile test_check_balance.py\n",
      "from nose.tools import assert_equal\n",
    "from nose.tools import raises\n",
      "\n",
      "\n",
      "class TestCheckBalance(object):\n",
      "\n",
      "    @raises(Exception)\n",
keep keep keep add keep keep keep keep keep
 Polish bst check balanced challenge and solution (#84)

Update constraints, tests, and code. 
graphs_trees/check_balance/check_balance_solution.ipynb