      "        hanoi(num_disks-1, buff, dest, src)"
     ]
    },
    {
     "cell_type": "code",
     "execution_count": 3,
     "metadata": {
      "collapsed": false
     },
 
</s> remove    "execution_count": null,
 </s> add    "execution_count": 3, </s> remove    "execution_count": null,
 </s> add    "execution_count": 2, </s> remove    "execution_count": null,
 </s> add    "execution_count": 1, </s> remove     "## Clarifying Questions\n",
 </s> add     "## Constraints and Assumptions\n", </s> remove     "print('NULL towers')\n",
    "hanoi(num_disks, None, None, None)\n",
    "first = Stack()\n",
    "second = Stack()\n",
    "third = Stack()\n",
    "print('0 disks')\n",
    "hanoi(num_disks, first, third, second)\n",
    "print('1 disk')\n",
    "first.push(5)\n",
    "hanoi(num_disks, first, third, second)\n",
    "print(third.pop())\n",
    "print('2 or more disks')\n",
    "num_disks = 3\n",
    "for i in xrange(num_disks, -1, -1):\n",
    "    first.push(i)\n",
    "hanoi(num_disks, first, third, second)\n",
    "for i in xrange(0, num_disks):\n",
    "    print(third.pop())"
 </s> add     "from nose.tools import assert_equal\n",
    "\n",
    "class Test(object):\n",
    "    def test_hanoi(self):\n",
    "        num_disks = 3\n",
    "        src = Stack()\n",
    "        buff = Stack()\n",
    "        dest = Stack()\n",
    "\n",
    "        print('Test: NULL towers')\n",
    "        hanoi(num_disks, None, None, None)\n",
    "\n",
    "        print('Test: 0 disks')\n",
    "        hanoi(num_disks, src, dest, buff)\n",
    "        assert_equal(dest.pop(), None)\n",
    "\n",
    "        print('Test: 1 disk')\n",
    "        src.push(5)\n",
    "        hanoi(num_disks, src, dest, buff)\n",
    "        assert_equal(dest.pop(), 5)\n",
    "\n",
    "        print('Test: 2 or more disks')\n",
    "        for i in xrange(num_disks, -1, -1):\n",
    "            src.push(i)\n",
    "        hanoi(num_disks, src, dest, buff)\n",
    "        for i in xrange(0, num_disks):\n",
    "            assert_equal(dest.pop(), i)\n",
    "\n",
    "        print('Success: test_hanoi')\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    test = Test()\n",
    "    test.test_hanoi()"
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test\n",
    "\n",
    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
   ]
  },
      "        hanoi(num_disks-1, buff, dest, src)"
     ]
    },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test\n",
    "\n",
    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
   ]
  },
    {
     "cell_type": "code",
     "execution_count": 3,
     "metadata": {
      "collapsed": false
     },
keep keep add keep keep keep keep keep keep
 Reworked notebook: Added more detail to constraints and test cases.  Reworked algorithm discussion and unit test. 
stacks-queues/hanoi.ipynb