lightning-talks/python-37-below-the-fold--mock-seal.ipynb

{
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   "source": [
    "# ⚡ Py3.7 Below the Fold: `mock.seal()` ⚡\n",
    "\n",
    "<br />or<br />\n",
    "\n",
    "# Lock Your Mock \n",
    "\n",
    "### Aly Sivji @CaiusSivjus\n",
    "### [bit.ly/lock-your-mock](http://bit.ly/lock-your-mock)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Problem with Mocks"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "notes"
    }
   },
   "source": [
    "Test doubles can be used to replace external dependencies with objects we create and define in order to write isolated unit tests.\n",
    "\n",
    "`unittest.mock` in the Python Standard Library is a popular mocking framework. It provides a flexible implementation of mock that simplifies the testing process."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [],
   "source": [
    "from unittest import mock"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<MagicMock name='my_mock' id='4476281688'>"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_mock = mock.MagicMock(name=\"my_mock\")\n",
    "my_mock"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "We can add attributes and functions to our `my_mock` object; this will return a new `MagicMock` object."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<MagicMock name='my_mock.new_attribute' id='4475565840'>"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_mock.new_attribute"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<MagicMock name='my_mock.new_function' id='4476436320'>"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_mock.new_function.return_value = 2\n",
    "my_mock.new_function"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_mock.new_function()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "We use mocks for behavior driven testing, i.e. we check that our mock was used how we think it was used."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "my_mock.new_function.assert_called_once()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_mock.new_function()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "Expected 'new_function' to have been called once. Called 2 times.",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-8-17f81fc5f28a>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mmy_mock\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mnew_function\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0massert_called_once\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m~/.pyenv/versions/3.7.0/lib/python3.7/unittest/mock.py\u001b[0m in \u001b[0;36massert_called_once\u001b[0;34m(_mock_self)\u001b[0m\n\u001b[1;32m    799\u001b[0m             msg = (\"Expected '%s' to have been called once. Called %s times.\" %\n\u001b[1;32m    800\u001b[0m                    (self._mock_name or 'mock', self.call_count))\n\u001b[0;32m--> 801\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mAssertionError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmsg\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    802\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    803\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0massert_called_with\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0m_mock_self\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m*\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m**\u001b[0m\u001b[0mkwargs\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mAssertionError\u001b[0m: Expected 'new_function' to have been called once. Called 2 times."
     ]
    }
   ],
   "source": [
    "my_mock.new_function.assert_called_once()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
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     "slide_type": "slide"
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   "source": [
    "### Beware\n",
    "\n",
    "Since we can create attributes / functions on demand, there is a possibility we can have tests pass with typos in our assert method."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<MagicMock name='my_mock.new_function.asert_called_once()' id='4477149592'>"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_mock.new_function.asert_called_once()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is returning another `MagicMock`, instead of raising an `AssertionError`."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "source": [
    "---"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## `mock.seal()`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "notes"
    }
   },
   "source": [
    "In Python 3.7, we can strictly define attributes and functions for mocks:\n",
    "\n",
    "> The new [`seal()`](https://docs.python.org/3/library/unittest.mock.html#unittest.mock.seal) function allows sealing [`Mock`](https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock) instances, which will disallow further creation of attribute mocks. The seal is applied recursively to all attributes that are themselves mocks. (Contributed by Mario Corchero in [bpo-30541](https://bugs.python.org/issue30541).)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<MagicMock name='sealed_mock' id='4477175232'>"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sealed_mock = mock.MagicMock(name=\"sealed_mock\")\n",
    "sealed_mock"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<MagicMock name='sealed_mock.only_function' id='4477187856'>"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sealed_mock.only_function.return_value = 2\n",
    "sealed_mock.only_function"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [],
   "source": [
    "mock.seal(sealed_mock)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "sealed_mock.new_function",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-13-10685e59d2cf>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0msealed_mock\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mnew_function\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m~/.pyenv/versions/3.7.0/lib/python3.7/unittest/mock.py\u001b[0m in \u001b[0;36m__getattr__\u001b[0;34m(self, name)\u001b[0m\n\u001b[1;32m    597\u001b[0m             result = self._get_child_mock(\n\u001b[1;32m    598\u001b[0m                 \u001b[0mparent\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mname\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mname\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mwraps\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mwraps\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0m_new_name\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mname\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 599\u001b[0;31m                 \u001b[0m_new_parent\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    600\u001b[0m             )\n\u001b[1;32m    601\u001b[0m             \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_mock_children\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mname\u001b[0m\u001b[0;34m]\u001b[0m  \u001b[0;34m=\u001b[0m \u001b[0mresult\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m~/.pyenv/versions/3.7.0/lib/python3.7/unittest/mock.py\u001b[0m in \u001b[0;36m_get_child_mock\u001b[0;34m(self, **kw)\u001b[0m\n\u001b[1;32m    903\u001b[0m             \u001b[0mattribute\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m\".\"\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0mkw\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m\"name\"\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;32mif\u001b[0m \u001b[0;34m\"name\"\u001b[0m \u001b[0;32min\u001b[0m \u001b[0mkw\u001b[0m \u001b[0;32melse\u001b[0m \u001b[0;34m\"()\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    904\u001b[0m             \u001b[0mmock_name\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_extract_mock_name\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0mattribute\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 905\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mAttributeError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmock_name\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    906\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    907\u001b[0m         \u001b[0;32mreturn\u001b[0m \u001b[0mklass\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m**\u001b[0m\u001b[0mkw\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mAttributeError\u001b[0m: sealed_mock.new_function"
     ]
    }
   ],
   "source": [
    "sealed_mock.new_function"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "notes"
    }
   },
   "source": [
    "Sealing our mock prevents the creation of unwanted attributes and methods!\n",
    "\n",
    "[Speccing](https://docs.python.org/3/library/unittest.mock.html#auto-speccing) solves the same problem by allowing us to create a mock that mirrors the attributes and methods of the real object.\n",
    "\n",
    "`mock.seal` afford us additional flexibility."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "source": [
    "---"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Additional Resources\n",
    "\n",
    "* [Python 3.7 What's New](https://docs.python.org/3/whatsnew/3.7.html)\n",
    "* [`unittest.mock.seal`](https://docs.python.org/3/library/unittest.mock.html#unittest.mock.seal)\n",
    "* [Issue 30541: Add restricted mocks to the python unittest mocking framework](https://bugs.python.org/issue30541)\n",
    "* [bit.ly/lock-your-mock](http://bit.ly/lock-your-mock)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "source": [
    "---"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Thank You\n",
    "\n",
    "* Github: [alysivji/talks](https://github.com/alysivji/talks)\n",
    "* Twitter: [@CaiusSivjus](https://twitter.com/CaiusSivjus)\n",
    "* Blog: [https://alysivji.github.io](https://alysivji.github.io)\n",
    "* Notebook: [http://bit.ly/siv-lightning-talks](https://github.com/alysivji/talks/tree/master/lightning-talks)"
   ]
  }
 ],
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