Scrapy Unit Testing

Question

I\'d like to implement some unit tests in a Scrapy (screen scraper/web crawler). Since a project is run through the \"scrapy crawl\" command I can run it through something

Answer 1

The newly added Spider Contracts are worth trying. It gives you a simple way to add tests without requiring a lot of code.

Answer 2

The way I've done it is create fake responses, this way you can test the parse function offline. But you get the real situation by using real HTML.

A problem with this approach is that your local HTML file may not reflect the latest state online. So if the HTML changes online you may have a big bug, but your test cases will still pass. So it may not be the best way to test this way.

My current workflow is, whenever there is an error I will sent an email to admin, with the url. Then for that specific error I create a html file with the content which is causing the error. Then I create a unittest for it.

This is the code I use to create sample Scrapy http responses for testing from an local html file:

# scrapyproject/tests/responses/__init__.py

import os

from scrapy.http import Response, Request

def fake_response_from_file(file_name, url=None):
    """
    Create a Scrapy fake HTTP response from a HTML file
    @param file_name: The relative filename from the responses directory,
                      but absolute paths are also accepted.
    @param url: The URL of the response.
    returns: A scrapy HTTP response which can be used for unittesting.
    """
    if not url:
        url = 'http://www.example.com'

    request = Request(url=url)
    if not file_name[0] == '/':
        responses_dir = os.path.dirname(os.path.realpath(__file__))
        file_path = os.path.join(responses_dir, file_name)
    else:
        file_path = file_name

    file_content = open(file_path, 'r').read()

    response = Response(url=url,
        request=request,
        body=file_content)
    response.encoding = 'utf-8'
    return response

The sample html file is located in scrapyproject/tests/responses/osdir/sample.html

Then the testcase could look as follows: The test case location is scrapyproject/tests/test_osdir.py

import unittest
from scrapyproject.spiders import osdir_spider
from responses import fake_response_from_file

class OsdirSpiderTest(unittest.TestCase):

    def setUp(self):
        self.spider = osdir_spider.DirectorySpider()

    def _test_item_results(self, results, expected_length):
        count = 0
        permalinks = set()
        for item in results:
            self.assertIsNotNone(item['content'])
            self.assertIsNotNone(item['title'])
        self.assertEqual(count, expected_length)

    def test_parse(self):
        results = self.spider.parse(fake_response_from_file('osdir/sample.html'))
        self._test_item_results(results, 10)

That's basically how I test my parsing methods, but its not only for parsing methods. If it gets more complex I suggest looking at Mox

Answer 3

I use Betamax to run test on real site the first time and keep http responses locally so that next tests run super fast after:

Betamax intercepts every request you make and attempts to find a matching request that has already been intercepted and recorded.

When you need to get latest version of site, just remove what betamax has recorded and re-run test.

Example:

from scrapy import Spider, Request
from scrapy.http import HtmlResponse


class Example(Spider):
    name = 'example'

    url = 'http://doc.scrapy.org/en/latest/_static/selectors-sample1.html'

    def start_requests(self):
        yield Request(self.url, self.parse)

    def parse(self, response):
        for href in response.xpath('//a/@href').extract():
            yield {'image_href': href}


# Test part
from betamax import Betamax
from betamax.fixtures.unittest import BetamaxTestCase


with Betamax.configure() as config:
    # where betamax will store cassettes (http responses):
    config.cassette_library_dir = 'cassettes'
    config.preserve_exact_body_bytes = True


class TestExample(BetamaxTestCase):  # superclass provides self.session

    def test_parse(self):
        example = Example()

        # http response is recorded in a betamax cassette:
        response = self.session.get(example.url)

        # forge a scrapy response to test
        scrapy_response = HtmlResponse(body=response.content, url=example.url)

        result = example.parse(scrapy_response)

        self.assertEqual({'image_href': u'image1.html'}, result.next())
        self.assertEqual({'image_href': u'image2.html'}, result.next())
        self.assertEqual({'image_href': u'image3.html'}, result.next())
        self.assertEqual({'image_href': u'image4.html'}, result.next())
        self.assertEqual({'image_href': u'image5.html'}, result.next())

        with self.assertRaises(StopIteration):
            result.next()

FYI, I discover betamax at pycon 2015 thanks to Ian Cordasco's talk.

Answer 4

https://github.com/ThomasAitken/Scrapy-Testmaster

This is a package I wrote that significantly extends the functionality of the Scrapy Autounit library and takes it in a different direction (allowing for easy dynamic updating of testcases and merging the processes of debugging/testcase-generation). It also includes a modified version of the Scrapy parse command (https://docs.scrapy.org/en/latest/topics/commands.html#std-command-parse)