编写你的第一个 Django 程序 第5部分

A test for a view

When we fixed the bug above, we wrote the test first and then the code to fix it. In fact that was a simple example of test-driven development, but it doesn’t really matter in which order we do the work.

In our first test, we focused closely on the internal behavior of the code. For this test, we want to check its behavior as it would be experienced by a user through a web browser.

Before we try to fix anything, let’s have a look at the tools at our disposal.

The Django test client

Django provides a test Client to simulate a user interacting with the code at the view level. We can use it in tests.py or even in the shell.

We will start again with the shell, where we need to do a couple of things that won’t be necessary in tests.py. The first is to set up the test environment in the shell:

>>> from django.test.utils import setup_test_environment
>>> setup_test_environment()

Next we need to import the test client class (later in tests.py we will use the django.test.TestCase class, which comes with its own client, so this won’t be required):

>>> from django.test.client import Client
>>> # create an instance of the client for our use
>>> client = Client()

With that ready, we can ask the client to do some work for us:

>>> # get a response from '/'
>>> response = client.get('/')
>>> # we should expect a 404 from that address
>>> response.status_code
404
>>> # on the other hand we should expect to find something at '/polls/'
>>> # we'll use 'reverse()' rather than a harcoded URL
>>> from django.core.urlresolvers import reverse
>>> response = client.get(reverse('polls:index'))
>>> response.status_code
200
>>> response.content
'\n\n\n    <p>No polls are available.</p>\n\n'
>>> # note - you might get unexpected results if your ``TIME_ZONE``
>>> # in ``settings.py`` is not correct. If you need to change it,
>>> # you will also need to restart your shell session
>>> from polls.models import Poll
>>> from django.utils import timezone
>>> # create a Poll and save it
>>> p = Poll(question="Who is your favorite Beatle?", pub_date=timezone.now())
>>> p.save()
>>> # check the response once again
>>> response = client.get('/polls/')
>>> response.content
'\n\n\n    <ul>\n    \n        <li><a href="/polls/1/">Who is your favorite Beatle?</a></li>\n    \n    </ul>\n\n'
>>> response.context['latest_poll_list']
[<Poll: Who is your favorite Beatle?>]

Improving our view

The list of polls shows polls that aren’t published yet (i.e. those that have a pub_date in the future). Let’s fix that.

In Tutorial 4 we deleted the view functions from views.py in favor of a ListView in urls.py:

url(r'^$',
    ListView.as_view(
        queryset=Poll.objects.order_by('-pub_date')[:5],
        context_object_name='latest_poll_list',
        template_name='polls/index.html'),
    name='index'),

response.context_data['latest_poll_list'] extracts the data this view places into the context.

We need to amend the line that gives us the queryset:

queryset=Poll.objects.order_by('-pub_date')[:5],

Let’s change the queryset so that it also checks the date by comparing it with timezone.now(). First we need to add an import:

from django.utils import timezone

and then we must amend the existing url function to:

url(r'^$',
    ListView.as_view(
        queryset=Poll.objects.filter(pub_date__lte=timezone.now) \
            .order_by('-pub_date')[:5],
        context_object_name='latest_poll_list',
        template_name='polls/index.html'),
    name='index'),

Poll.objects.filter(pub_date__lte=timezone.now) returns a queryset containing Polls whose pub_date is less than or equal to - that is, earlier than or equal to - timezone.now. Notice that we use a callable queryset argument, timezone.now, which will be evaluated at request time. If we had included the parentheses, timezone.now() would be evaluated just once when the web server is started.