Basic testing strategiesThere 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 testWe identify a bugFortunately, there’s a little bug in the You can see this in the Admin; create a poll whose date lies in the future; you’ll see that the 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 bugWhat 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 Put the following in the 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 Running testsIn 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:
The test informs us which test failed and even the line on which the failure occurred. Fixing the bugWe already know what the problem is: 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. |
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