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Making Django and Lettuce play nice together

Lettuce is a great BDD tool which allows you to parse expressions written via Gherkin syntax in python. However the documentation is not very comprehensive, and at the moment current version (0.2.19) has some issues integrating with the latest Django (1.6.1 at the moment of writing). Without further ado, I’ll get to a comprehensive tutorial.

Let’s assume you are using pip and virtualenv for the dependency control, and you already have a working project configured. Your project is called “myproject”, and the only app you have within your project is called “polls”.

Setup

First, you have to install lettuce library. At the moment of writing, current released version (0.2.19) has an error integrating with Django, so we’ll install current development version. Releases 0.2.20 and up should include the fix, so pip install lettuce would be better if the version is out.

pip install -e \
    git://github.com/gabrielfalcao/lettuce@cccc397#egg=lettuce-master
pip install django-nose splinter
pip freeze > requirements.txt

First line downloads lettuce package from the github repository and installs missing dependencies. You can replace cccc397 with the current commit. Technically commit can be omitted, but we don’t want to have an unstable ever-changing branch in our requirements.txt. I also added django-nose since nose assertions come in handy while writing Lettuce steps, as well as splinter, which is a great tool for testing web application.

Add Lettuce to the INSTALLED_APPS in your myproject/settings.py:

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'django.contrib.admin',
    'django.contrib.admindocs',
    # ... third party apps ...
    'lettuce.django',
    'myproject',
    'polls',
)

You also have to explicitly specify the apps you want to use with lettuce:

LETTUCE_APPS = (
    'polls',
)

By default, lettuce will run its’ tests against your default database. But we want to use test database for that, so we have to add few more settings:

LETTUCE_TEST_SERVER = 'lettuce.django.server.DjangoServer'
LETTUCE_SERVER_PORT = 9000

Where LETTUCE_TEST_SERVER is a subclass of Django’s LiveTestServerCase - a class which runs a test server for you and LETTUCE_SERVER_PORT is different from port 8000 so you won’t have issues running the development server via python manage.py runserver at the same time as running Lettuce tests.

You also have to create a features directories inside the apps you want to test with Lettuce:

/myproject
    /myproject
        __init__.py
        settings.py
        urls.py
        wsgi.py
    /polls
        /features
            /steps
                __init__.py
                polls_list.py
            polls_list.feature
        __init__.py
        models.py
        tests.py
        views.py
    manage.py
    requirements.txt
    terrain.py

Lettuce has its’ own settings file called terrain.py. It has to be in the same directory as a manage.py:

from django.core.management import call_command
from django.conf import settings
from lettuce import before, after, world
from splinter.browser import Browser

@before.each_scenario
def flush_database(scenario):
    call_command('flush', interactive=False, verbosity=0)

@before.each_scenario
def prepare_browser(scenario):
    world.browser = Browser()

@after.each_scenario
def destroy_browser(scenario):
    world.browser.quit()

This code flushes the database before each scenario, as well as prepares and destroys the splinter browser.

Writing the features

Feature files support standard Gherkin syntax, let’s write one right now in polls/features/polls_list.feature:

Feature: Polls list

    Scenario: Polls list without any polls
        When I access the "polls list" url
        Then I see a text "We didn't find any polls!"

    Scenario: Polls list with one poll
        Given a poll with the title "Hello world"
        When I access the "polls list" url
        Then I see a text "Hello world"
        And I do not see a text "We didn't find any polls!"

Now describe the steps in polls/features/steps/polls_list.py:

from django.core.urlresolvers import reverse
from lettuce import step, world
from lettuce.django import django_url
from nose.tools import assert_in, assert_not_in
from polls.models import Poll

PAGES = {
    "polls list": "polls:list"
}

@step(r'access the "(.*)" url')
def access_the_url(step, name):
    world.browser.visit(django_url(reverse(PAGES[name])))

@step(r'see a text "(.*)"')
def see_a_text(step, text):
    assert_in(text, world.browser.html)

@step(r'a poll with the title "(.*)"')
def create_a_poll_with_the_title(step, title):
    poll = Poll.objects.create(title=title)
    polls.save()

@step(r'do not see a text "(.*)"')
def do_not_see_a_text(step, text):
    assert_not_in(text, world.browser.html)

Running the tests

Now, you can run python manage.py harvest --test-server to run the tests you just wrote:

$ python manage.py harvest --test-server
Creating test database for alias 'default'...
Django's builtin server is running at 0.0.0.0:9000

Feature: Polls list

  Scenario: Polls list without any polls
    When I access the "polls list" url
    Then I see a text "We didn't find any polls!"

  Scenario: Polls list with one poll
    Given a poll with the title "Hello world"
    When I access the "polls list" url
    Then I see a text "Hello world"
    And I do not see a text "We didn't find any polls!"

1 feature (1 passed)
2 scenarios (2 passed)
6 steps (6 passed)
Destroying test database for alias 'default'...

Don’t forget the --test-server switch - otherwise Lettuce will run tests against your default database.

Sources

You can find some more details on Lettuce and Django integration here: Web development fun with Lettuce and Django.

Update

Rather than using --test-server switch, it’s easier and safer to set a flag in your settings.py (suggested by Michel Sabchuk):

LETTUCE_USE_TEST_DATABASE = True

This way you won’t end up accidentally erasing your production database after forgetting to add --test-server flag.

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