编写你的第一个 Django 程序 第5部分¶

什么是自动化测试？¶

测试是用于检测你的代码运行是否正确的简单程序。

测试操作分不同的级别。有些人可能只测试小的细节 - 测试一个模型方法返回的值 是否如预期一样？ ， 而其他人则检测软件的整体运行是否正确 - 检测用户在网站上的一系列操作产生的结果正确与否？ 这其实和前面 教程 第1部分 中的方法没有什么不同，就是使用 shell 检查方法的行为，或者运行程序并输入数据来检查它的行为方式。

自动化测试 的不同之处就在由系统为你完成测试工作。你一旦创建了一组测试案例，当你修改了你的 应用，你就可以检查你的代码是否仍然同预期的那样运行，而无需执行耗时的手动测试。

为什么你需要创建测试¶

那么为什么要创建测试？而且是现在呢？

你可能感觉学习 Python/Django 已经足够了，再去学习其他的东西也许没有必要。 毕竟，我们的投票应用现在正常运行；而通过创建自动测试会使其运行得更好。 如果创建的投票应用的是通过 Django 编程实现的，你从始至终都是这样做的，若是真的，那么你 不需要知道如何创建自动化测试。但是如果不是这样的话，现在是一个很好的学习时间。

We identify a bug¶

Fortunately, there’s a little bug in the polls application for us to fix right away: the Poll.was_published_recently() method returns True if the Poll was published within the last day (which is correct) but also if the Poll‘s pub_date field is in the future (which certainly isn’t).

You can see this in the Admin; create a poll whose date lies in the future; you’ll see that the Poll change list claims it was published recently.

You can also see this using the shell:

>>> import datetime
>>> from django.utils import timezone
>>> from polls.models import Poll
>>> # create a Poll instance with pub_date 30 days in the future
>>> future_poll = Poll(pub_date=timezone.now() + datetime.timedelta(days=30))
>>> # was it published recently?
>>> future_poll.was_published_recently()
True

Since things in the future are not ‘recent’, this is clearly wrong.

Create a test to expose the bug¶

What we’ve just done in the shell to test for the problem is exactly what we can do in an automated test, so let’s turn that into an automated test.

The best place for an application’s tests is in the application’s tests.py file - the testing system will look there for tests automatically.

Put the following in the tests.py file in the polls application (you’ll notice tests.py contains some dummy tests, you can remove those):

import datetime

from django.utils import timezone
from django.test import TestCase

from polls.models import Poll

class PollMethodTests(TestCase):

    def test_was_published_recently_with_future_poll(self):
        """
        was_published_recently() should return False for polls whose
        pub_date is in the future
        """
        future_poll = Poll(pub_date=timezone.now() + datetime.timedelta(days=30))
        self.assertEqual(future_poll.was_published_recently(), False)

What we have done here is created a django.test.TestCase subclass with a method that creates a Poll instance with a pub_date in the future. We then check the output of was_published_recently() - which ought to be False.

Running tests¶

In the terminal, we can run our test:

python manage.py test polls

and you’ll see something like:

Creating test database for alias 'default'...
F
======================================================================
FAIL: test_was_published_recently_with_future_poll (polls.tests.PollMethodTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/path/to/mysite/polls/tests.py", line 16, in test_was_published_recently_with_future_poll
    self.assertEqual(future_poll.was_published_recently(), False)
AssertionError: True != False

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)
Destroying test database for alias 'default'...

What happened is this:

• python manage.py test polls looked for tests in the polls application
• it found a subclass of the django.test.TestCase class
• it created a special database for the purpose of testing
• it looked for test methods - ones whose names begin with test
• in test_was_published_recently_with_future_poll it created a Poll instance whose pub_date field is 30 days in the future
• ... and using the assertEqual() method, it discovered that its was_published_recently() returns True, though we wanted it to return False

The test informs us which test failed and even the line on which the failure occurred.

Fixing the bug¶

We already know what the problem is: Poll.was_published_recently() should return False if its pub_date is in the future. Amend the method in models.py, so that it will only return True if the date is also in the past:

def was_published_recently(self):
    now = timezone.now()
    return now - datetime.timedelta(days=1) <= self.pub_date <  now

and run the test again:

Creating test database for alias 'default'...
.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK
Destroying test database for alias 'default'...

After identifying a bug, we wrote a test that exposes it and corrected the bug in the code so our test passes.

Many other things might go wrong with our application in the future, but we can be sure that we won’t inadvertently reintroduce this bug, because simply running the test will warn us immediately. We can consider this little portion of the application pinned down safely forever.

More comprehensive tests¶

While we’re here, we can further pin down the was_published_recently() method; in fact, it would be positively embarrassing if in fixing one bug we had introduced another.

Add two more test methods to the same class, to test the behavior of the method more comprehensively:

def test_was_published_recently_with_old_poll(self):
    """
    was_published_recently() should return False for polls whose pub_date
    is older than 1 day
    """
    old_poll = Poll(pub_date=timezone.now() - datetime.timedelta(days=30))
    self.assertEqual(old_poll.was_published_recently(), False)

def test_was_published_recently_with_recent_poll(self):
    """
    was_published_recently() should return True for polls whose pub_date
    is within the last day
    """
    recent_poll = Poll(pub_date=timezone.now() - datetime.timedelta(hours=1))
    self.assertEqual(recent_poll.was_published_recently(), True)

And now we have three tests that confirm that Poll.was_published_recently() returns sensible values for past, recent, and future polls.

Again, polls is a simple application, but however complex it grows in the future and whatever other code it interacts with, we now have some guarantee that the method we have written tests for will behave in expected ways.

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.

Testing our new view¶

Now you can satisfy yourself that this behaves as expected by firing up the runserver, loading the site in your browser, creating Polls with dates in the past and future, and checking that only those that have been published are listed. You don’t want to have to do that every single time you make any change that might affect this - so let’s also create a test, based on our shell session above.

Add the following to polls/tests.py:

from django.core.urlresolvers import reverse

and we’ll create a factory method to create polls as well as a new test class:

def create_poll(question, days):
    """
    Creates a poll with the given `question` published the given number of
    `days` offset to now (negative for polls published in the past,
    positive for polls that have yet to be published).
    """
    return Poll.objects.create(question=question,
        pub_date=timezone.now() + datetime.timedelta(days=days))

class PollViewTests(TestCase):
    def test_index_view_with_no_polls(self):
        """
        If no polls exist, an appropriate message should be displayed.
        """
        response = self.client.get(reverse('polls:index'))
        self.assertEqual(response.status_code, 200)
        self.assertContains(response, "No polls are available.")
        self.assertQuerysetEqual(response.context['latest_poll_list'], [])

    def test_index_view_with_a_past_poll(self):
        """
        Polls with a pub_date in the past should be displayed on the index page.
        """
        create_poll(question="Past poll.", days=-30)
        response = self.client.get(reverse('polls:index'))
        self.assertQuerysetEqual(
            response.context['latest_poll_list'],
            ['<Poll: Past poll.>']
        )

    def test_index_view_with_a_future_poll(self):
        """
        Polls with a pub_date in the future should not be displayed on the
        index page.
        """
        create_poll(question="Future poll.", days=30)
        response = self.client.get(reverse('polls:index'))
        self.assertContains(response, "No polls are available.", status_code=200)
        self.assertQuerysetEqual(response.context['latest_poll_list'], [])

    def test_index_view_with_future_poll_and_past_poll(self):
        """
        Even if both past and future polls exist, only past polls should be
        displayed.
        """
        create_poll(question="Past poll.", days=-30)
        create_poll(question="Future poll.", days=30)
        response = self.client.get(reverse('polls:index'))
        self.assertQuerysetEqual(
            response.context['latest_poll_list'],
            ['<Poll: Past poll.>']
        )

    def test_index_view_with_two_past_polls(self):
        """
        The polls index page may display multiple polls.
        """
        create_poll(question="Past poll 1.", days=-30)
        create_poll(question="Past poll 2.", days=-5)
        response = self.client.get(reverse('polls:index'))
        self.assertQuerysetEqual(
            response.context['latest_poll_list'],
             ['<Poll: Past poll 2.>', '<Poll: Past poll 1.>']
        )

Let’s look at some of these more closely.

First is a poll factory method, create_poll, to take some repetition out of the process of creating polls.

test_index_view_with_no_polls doesn’t create any polls, but checks the message: “No polls are available.” and verifies the latest_poll_list is empty. Note that the django.test.TestCase class provides some additional assertion methods. In these examples, we use assertContains() and assertQuerysetEqual().

In test_index_view_with_a_past_poll, we create a poll and verify that it appears in the list.

In test_index_view_with_a_future_poll, we create a poll with a pub_date in the future. The database is reset for each test method, so the first poll is no longer there, and so again the index shouldn’t have any polls in it.

And so on. In effect, we are using the tests to tell a story of admin input and user experience on the site, and checking that at every state and for every new change in the state of the system, the expected results are published.

Testing the DetailView¶

What we have works well; however, even though future polls don’t appear in the index, users can still reach them if they know or guess the right URL. So we need similar constraints in the DetailViews, by adding:

queryset=Poll.objects.filter(pub_date__lte=timezone.now)

to them - for example:

url(r'^(?P<pk>\d+)/$',
    DetailView.as_view(
        queryset=Poll.objects.filter(pub_date__lte=timezone.now),
        model=Poll,
        template_name='polls/detail.html'),
    name='detail'),

and of course, we will add some tests, to check that a Poll whose pub_date is in the past can be displayed, and that one with a pub_date in the future is not:

class PollIndexDetailTests(TestCase):
    def test_detail_view_with_a_future_poll(self):
        """
        The detail view of a poll with a pub_date in the future should
        return a 404 not found.
        """
        future_poll = create_poll(question='Future poll.', days=5)
        response = self.client.get(reverse('polls:detail', args=(future_poll.id,)))
        self.assertEqual(response.status_code, 404)

    def test_detail_view_with_a_past_poll(self):
        """
        The detail view of a poll with a pub_date in the past should display
        the poll's question.
        """
        past_poll = create_poll(question='Past Poll.', days=-5)
        response = self.client.get(reverse('polls:detail', args=(past_poll.id,)))
        self.assertContains(response, past_poll.question, status_code=200)

Ideas for more tests¶

We ought to add similar queryset arguments to the other DetailView URLs, and create a new test class for each view. They’ll be very similar to what we have just created; in fact there will be a lot of repetition.

We could also improve our application in other ways, adding tests along the way. For example, it’s silly that Polls can be published on the site that have no Choices. So, our views could check for this, and exclude such Polls. Our tests would create a Poll without Choices and then test that it’s not published, as well as create a similar Poll with Choices, and test that it is published.

Perhaps logged-in admin users should be allowed to see unpublished Polls, but not ordinary visitors. Again: whatever needs to be added to the software to accomplish this should be accompanied by a test, whether you write the test first and then make the code pass the test, or work out the logic in your code first and then write a test to prove it.

At a certain point you are bound to look at your tests and wonder whether your code is suffering from test bloat, which brings us to: