编写你的第一个 Django 程序 第5部分¶
本教程上接 教程 第4部分 。 我们已经建立了一个 Web-poll 应用，现在我们会为它创建一些自动化测试。
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。
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。
在这些组件中的任何修改对应用的行为都可能产生意想不到的后果。 检查应用仍然’似乎运行正常’可能意味着你的测试数据经过你的代码中二十多种变化功能后只是为了确保 你没有破坏它们 - 没有很好地利用你的时间。
Sometimes it may seem a chore to tear yourself away from your productive, creative programming work to face the unglamorous and unexciting business of writing tests, particularly when you know your code is working properly.
However, the task of writing tests is a lot more fulfilling than spending hours testing your application manually or trying to identify the cause of a newly-introduced problem.
Tests don’t just identify problems, they prevent them¶
It’s a mistake to think of tests merely as a negative aspect of development.
Without tests, the purpose or intended behavior of an application might be rather opaque. Even when it’s your own code, you will sometimes find yourself poking around in it trying to find out what exactly it’s doing.
Tests change that; they light up your code from the inside, and when something goes wrong, they focus light on the part that has gone wrong - even if you hadn’t even realized it had gone wrong.
Tests make your code more attractive¶
You might have created a brilliant piece of software, but you will find that many other developers will simply refuse to look at it because it lacks tests; without tests, they won’t trust it. Jacob Kaplan-Moss, one of Django’s original developers, says “Code without tests is broken by design.”
That other developers want to see tests in your software before they take it seriously is yet another reason for you to start writing tests.
Tests help teams work together¶
The previous points are written from the point of view of a single developer maintaining an application. Complex applications will be maintained by teams. Tests guarantee that colleagues don’t inadvertently break your code (and that you don’t break theirs without knowing). If you want to make a living as a Django programmer, you must be good at writing tests!
Basic testing strategies¶
There are many ways to approach writing tests.
Some programmers follow a discipline called “test-driven development”; they actually write their tests before they write their code. This might seem counter-intuitive, but in fact it’s similar to what most people will often do anyway: they describe a problem, then create some code to solve it. Test-driven development simply formalizes the problem in a Python test case.
More often, a newcomer to testing will create some code and later decide that it should have some tests. Perhaps it would have been better to write some tests earlier, but it’s never too late to get started.
Sometimes it’s difficult to figure out where to get started with writing tests. If you have written several thousand lines of Python, choosing something to test might not be easy. In such a case, it’s fruitful to write your first test the next time you make a change, either when you add a new feature or fix a bug.
So let’s do that right away.
Writing our first test¶
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
Poll was published within the last day (which is correct) but also if
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
file - the testing system will look there for tests automatically.
Put the following in the
tests.py file in the
polls application (you’ll
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
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.
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 pollslooked for tests in the
- it found a subclass of the
- it created a special database for the purpose of testing
- it looked for test methods - ones whose names begin with
test_was_published_recently_with_future_pollit created a
pub_datefield is 30 days in the future
- ... and using the
assertEqual()method, it discovered that its
True, though we wanted it to return
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:
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
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
method; in fact, it would be positively embarrassing if in fixing one bug we had
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
returns sensible values for past, recent, and future polls.
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.
Test a view¶
The polls application is fairly undiscriminating: it will publish any poll,
including ones whose
pub_date field lies in the future. We should improve
this. Setting a
pub_date in the future should mean that the Poll is
published at that moment, but invisible until then.
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
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
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
url(r'^$', ListView.as_view( queryset=Poll.objects.order_by('-pub_date')[:5], context_object_name='latest_poll_list', template_name='polls/index.html'), name='index'),
response.context_data['latest_poll_list'] extracts the data this view
places into the context.
We need to amend the line that gives us the
Let’s change the queryset so that it also checks the date by comparing it with
timezone.now(). First we need to add an import:
from django.utils import timezone
and then we must amend the existing
url function to:
url(r'^$', 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
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
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
empty. Note that the
django.test.TestCase class provides some
additional assertion methods. In these examples, we use
test_index_view_with_a_past_poll, we create a poll and verify that it
appears in the list.
test_index_view_with_a_future_poll, we create a poll with a
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.
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:
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
pub_date is in the past can be displayed, and that one with a
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
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
Choices. So, our views could check for this, and exclude such
Polls. Our tests would create a
Choices and then test
that it’s not published, as well as create a similar
Choices, and test that it is published.
Perhaps logged-in admin users should be allowed to see unpublished
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:
When testing, more is better¶
It might seem that our tests are growing out of control. At this rate there will soon be more code in our tests than in our application, and the repetition is unaesthetic, compared to the elegant conciseness of the rest of our code.
It doesn’t matter. Let them grow. For the most part, you can write a test once and then forget about it. It will continue performing its useful function as you continue to develop your program.
Sometimes tests will need to be updated. Suppose that we amend our views so that
Choices are published. In that case, many of our
existing tests will fail - telling us exactly which tests need to be amended to
bring them up to date, so to that extent tests help look after themselves.
At worst, as you continue developing, you might find that you have some tests that are now redundant. Even that’s not a problem; in testing redundancy is a good thing.
As long as your tests are sensibly arranged, they won’t become unmanageable. Good rules-of-thumb include having:
- a separate
TestClassfor each model or view
- a separate test method for each set of conditions you want to test
- test method names that describe their function
This tutorial only introduces some of the basics of testing. There’s a great deal more you can do, and a number of very useful tools at your disposal to achieve some very clever things.
For example, while our tests here have covered some of the internal logic of a
model and the way our views publish information, you can use an “in-browser”
framework such as Selenium to test the way your HTML actually renders in a
browser. These tools allow you to check not just the behavior of your Django
the tests launch a browser, and start interacting with your site, as if a human
being were driving it! Django includes
to facilitate integration with tools like Selenium.
If you have a complex application, you may want to run tests automatically with every commit for the purposes of continuous integration, so that quality control is itself - at least partially - automated.
A good way to spot untested parts of your application is to check code coverage. This also helps identify fragile or even dead code. If you can’t test a piece of code, it usually means that code should be refactored or removed. Coverage will help to identify dead code. See Integration with coverage.py for details.
Testing Django applications has comprehensive information about testing.
The beginner tutorial ends here for the time being. In the meantime, you might want to check out some pointers on where to go from here.
If you are familiar with Python packaging and interested in learning how to turn polls into a “reusable app”, check out Advanced tutorial: How to write reusable apps.