Development with Python

2. At the time of writing, the latest Selenium (2.41) was causing me

so that’s why I’m pinning it

to 2.39 here. By all means experiment with newer versions!

Destroying test database for alias 'default'...

+ python manage.py test functional_tests

ImportError: No module named 'selenium'

Build step 'Virtualenv Builder' marked build as failure

Ah. We need Selenium in our virtualenv.

Let’s add a manual installation of Selenium to our build steps:

pip install -r requirements.txt

pip install selenium==2.39

python manage.py test accounts lists

python manage.py test functional_tests

Some people like to use a file called

test-requirements.txt

specify packages that are needed for the tests, but not the

main app.

Now what?

File

"/var/lib/jenkins/shiningpanda/jobs/ddc1aed1/virtualenvs/d41d8cd9/lib/python3.

line 100, in _wait_until_connectable

self._get_firefox_output())

selenium.common.exceptions.WebDriverException: Message: 'The browser appears to

have exited before we could connect. The output was: b"\\n(process:19757):

GLib-CRITICAL **: g_slice_set_config: assertion \'sys_page_size == 0\'

failed\\nError: no display specified\\n"'

Setting Up a Virtual Display so the FTs Can Run Headless

As you can see from the traceback, Firefox is unable to start because the server doesn’t

have a display.

There are two ways to deal with this problem. The first is to switch to using a headless

browser, like PhantomJS or SlimerJS. Those tools definitely have their place—they’re

faster, for one thing—but they also have disadvantages. The first is that they’re not “real”

web browsers, so you can’t be sure you’re going to catch all the strange quirks and

behaviours of the actual browsers your users use. The second is that they behave quite

differently inside Selenium, and will require substantial amounts of rewriting of FT

code.

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Chapter 20: Continuous Integration (CI)