diff --git a/docs/index.txt b/docs/index.txt index e6eb77c98f..9fea8ff3f2 100644 --- a/docs/index.txt +++ b/docs/index.txt @@ -44,7 +44,8 @@ Are you new to Django or to programming? This is the place to start! :doc:`Part 1 ` | :doc:`Part 2 ` | :doc:`Part 3 ` | - :doc:`Part 4 ` + :doc:`Part 4 ` | + :doc:`Part 5 ` * **Advanced Tutorials:** :doc:`How to write reusable apps ` | diff --git a/docs/intro/index.txt b/docs/intro/index.txt index bca2d7712b..ea6a3c4d29 100644 --- a/docs/intro/index.txt +++ b/docs/intro/index.txt @@ -13,6 +13,7 @@ place: read this material to quickly get up and running. tutorial02 tutorial03 tutorial04 + tutorial05 reusable-apps whatsnext contributing diff --git a/docs/intro/reusable-apps.txt b/docs/intro/reusable-apps.txt index 11a441d277..6aade4997e 100644 --- a/docs/intro/reusable-apps.txt +++ b/docs/intro/reusable-apps.txt @@ -2,11 +2,11 @@ Advanced tutorial: How to write reusable apps ============================================= -This advanced tutorial begins where :doc:`Tutorial 4 ` left +This advanced tutorial begins where :doc:`Tutorial 5 ` left off. We'll be turning our Web-poll into a standalone Python package you can reuse in new projects and share with other people. -If you haven't recently completed Tutorials 1–4, we encourage you to review +If you haven't recently completed Tutorials 1–5, we encourage you to review these so that your example project matches the one described below. Reusability matters diff --git a/docs/intro/tutorial04.txt b/docs/intro/tutorial04.txt index dfee827056..1619b599bb 100644 --- a/docs/intro/tutorial04.txt +++ b/docs/intro/tutorial04.txt @@ -275,13 +275,5 @@ Run the server, and use your new polling app based on generic views. For full details on generic views, see the :doc:`generic views documentation `. -What's next? -============ - -The beginner tutorial ends here for the time being. In the meantime, you might -want to check out some pointers on :doc:`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 :doc:`Advanced tutorial: How to -write reusable apps`. +When you're comfortable with forms and generic views, read :doc:`part 5 of this +tutorial` to learn about testing our polls app. diff --git a/docs/intro/tutorial05.txt b/docs/intro/tutorial05.txt new file mode 100644 index 0000000000..163b7cdd0f --- /dev/null +++ b/docs/intro/tutorial05.txt @@ -0,0 +1,650 @@ +===================================== +Writing your first Django app, part 5 +===================================== + +This tutorial begins where :doc:`Tutorial 4 ` left off. +We've built a Web-poll application, and we'll now create some automated tests +for it. + +Introducing automated testing +============================= + +What are automated tests? +------------------------- + +Tests are simple routines that check the operation of your code. + +Testing operates at different levels. Some tests might apply to a tiny detail +- *does a particular model method return values as expected?*, while others +examine the overall operation of the software - *does a sequence of user inputs +on the site produce the desired result?* That's no different from the kind of +testing you did earlier in :doc:`Tutorial 1 `, using the +shell to examine the behavior of a method, or running the application and +entering data to check how it behaves. + +What's different in *automated* tests is that the testing work is done for +you by the system. You create a set of tests once, and then as you make changes +to your app, you can check that your code still works as you originally +intended, without having to perform time consuming manual testing. + +Why you need to create tests +---------------------------- + +So why create tests, and why now? + +You may feel that you have quite enough on your plate just learning +Python/Django, and having yet another thing to learn and do may seem +overwhelming and perhaps unnecessary. After all, our polls application is +working quite happily now; going through the trouble of creating automated +tests is not going to make it work any better. If creating the polls +application is the last bit of Django programming you will ever do, then true, +you don't need to know how to create automated tests. But, if that's not the +case, now is an excellent time to learn. + +Tests will save you time +~~~~~~~~~~~~~~~~~~~~~~~~ + +Up to a certain point, 'checking that it seems to work' will be a satisfactory +test. In a more sophisticated application, you might have dozens of complex +interactions between components. + +A change in any of those components could have unexpected consequences on the +application's behavior. Checking that it still 'seems to work' could mean +running through your code's functionality with twenty different variations of +your test data just to make sure you haven't broken something - not a good use +of your time. + +That's especially true when automated tests could do this for you in seconds. +If something's gone wrong, tests will also assist in identifying the code +that's causing the unexpected behavior. + +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. + +.. _test-driven development: http://en.wikipedia.org/wiki/Test-driven_development/ + +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 ``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 :class:`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 :class:`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. + +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 :class:`~django.test.client.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 :class:`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

No polls are available.

\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 \n\n' + >>> response.context['latest_poll_list'] + [] + +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 :doc:`Tutorial 4 ` we deleted the view functions from +``views.py`` in favor of a :class:`~django.views.generic.list.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'], + [''] + ) + + 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'], + [''] + ) + + 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'], + ['', ''] + ) + +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 :class:`django.test.TestCase` class provides some +additional assertion methods. In these examples, we use +:meth:`~django.test.TestCase.assertContains()` and +:meth:`~django.test.TestCase.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\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: + +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 +only ``Polls`` with ``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 ``TestClass`` for each model or view +* a separate test method for each set of conditions you want to test +* test method names that describe their function + +Further testing +=============== + +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 +code, but also, for example, of your JavaScript. It's quite something to see +the tests launch a browser, and start interacting with your site, as if a human +being were driving it! Django includes :class:`~django.test.LiveServerTestCase` +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 +:ref:`topics-testing-code-coverage` for details. + +:doc:`Testing Django applications ` has comprehensive +information about testing. + +.. _Selenium: http://seleniumhq.org/ +.. _continuous integration: http://en.wikipedia.org/wiki/Continuous_integration + +What's next? +============ + +The beginner tutorial ends here for the time being. In the meantime, you might +want to check out some pointers on :doc:`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 :doc:`Advanced tutorial: How to +write reusable apps`.