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   "source": [
    "> This is one of the 100 recipes of the [IPython Cookbook](http://ipython-books.github.io/), the definitive guide to high-performance scientific computing and data science in Python.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 2.7. Writing unit tests with nose\n",
    "\n",
    "**This is the Python 3 version of the recipe.**\n",
    "\n",
    "Although Python has a native unit testing module (unittest), we will rather use Nose which is more convenient and more powerful. Having an extra dependency is not a problem as the Nose package is only required to launch the test suite, and not to use the software itself."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Creation of the Python module"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "%%writefile datautils.py\n",
    "# Version 1.\n",
    "import os\n",
    "from urllib.request import urlopen  # Python 2: use urllib2\n",
    "\n",
    "def download(url):\n",
    "    \"\"\"Download a file and save it in the current folder.\n",
    "    Return the name of the downloaded file.\"\"\"\n",
    "    # Get the filename.\n",
    "    file = os.path.basename(url)\n",
    "    # Download the file unless it already exists.\n",
    "    if not os.path.exists(file):\n",
    "        with open(file, 'w') as f:\n",
    "            f.write(urlopen(url).read())\n",
    "    return file"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Creation of the test module"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "%%writefile test_datautils.py\n",
    "from urllib.request import (HTTPHandler, install_opener, \n",
    "                            build_opener, addinfourl)\n",
    "import os\n",
    "import shutil\n",
    "import tempfile\n",
    "from io import StringIO  # Python 2: use StringIO\n",
    "from datautils import download\n",
    "\n",
    "TEST_FOLDER = tempfile.mkdtemp()\n",
    "ORIGINAL_FOLDER = os.getcwd()\n",
    "\n",
    "class TestHTTPHandler(HTTPHandler):\n",
    "    \"\"\"Mock HTTP handler.\"\"\"\n",
    "    def http_open(self, req):\n",
    "        resp = addinfourl(StringIO('test'), '', req.get_full_url(), 200)\n",
    "        resp.msg = 'OK'\n",
    "        return resp\n",
    "    \n",
    "def setup():\n",
    "    \"\"\"Install the mock HTTP handler for unit tests.\"\"\"\n",
    "    install_opener(build_opener(TestHTTPHandler))\n",
    "    os.chdir(TEST_FOLDER)\n",
    "    \n",
    "def teardown():\n",
    "    \"\"\"Restore the normal HTTP handler.\"\"\"\n",
    "    install_opener(build_opener(HTTPHandler))\n",
    "    # Go back to the original folder.\n",
    "    os.chdir(ORIGINAL_FOLDER)\n",
    "    # Delete the test folder.\n",
    "    shutil.rmtree(TEST_FOLDER)\n",
    "\n",
    "def test_download1():\n",
    "    file = download(\"http://example.com/file.txt\")\n",
    "    # Check that the file has been downloaded.\n",
    "    assert os.path.exists(file)\n",
    "    # Check that the file contains the contents of the remote file.\n",
    "    with open(file, 'r') as f:\n",
    "        contents = f.read()\n",
    "    print(contents)\n",
    "    assert contents == 'test'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Launching the tests"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "!nosetests"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Adding a failing test"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now, let's add a new test."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "%%writefile test_datautils.py -a\n",
    "\n",
    "def test_download2():\n",
    "    file = download(\"http://example.com/\")\n",
    "    assert os.path.exists(file)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "!nosetests"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Fixing the failing test"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The new test fails because the filename cannot be inferred from the URL, so we need to handle this case."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "%%writefile datautils.py\n",
    "# Version 2.\n",
    "import os\n",
    "from urllib.request import urlopen  # Python 2: use urllib2\n",
    "\n",
    "def download(url):\n",
    "    \"\"\"Download a file and save it in the current folder.\n",
    "    Return the name of the downloaded file.\"\"\"\n",
    "    # Get the filename.\n",
    "    file = os.path.basename(url)\n",
    "    # Fix the bug, by specifying a fixed filename if the URL \n",
    "    # does not contain one.\n",
    "    if not file:\n",
    "        file = 'downloaded'\n",
    "    # Download the file unless it already exists.\n",
    "    if not os.path.exists(file):\n",
    "        with open(file, 'w') as f:\n",
    "            f.write(urlopen(url).read())\n",
    "    return file"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "!nosetests"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "> You'll find all the explanations, figures, references, and much more in the book (to be released later this summer).\n",
    "\n",
    "> [IPython Cookbook](http://ipython-books.github.io/), by [Cyrille Rossant](http://cyrille.rossant.net), Packt Publishing, 2014 (500 pages)."
   ]
  }
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