diff -r 5ff1fc726848 -r c6bca38c1cbf parts/django/docs/topics/testing.txt --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/parts/django/docs/topics/testing.txt Sat Jan 08 11:20:57 2011 +0530 @@ -0,0 +1,1613 @@ +=========================== +Testing Django applications +=========================== + +.. module:: django.test + :synopsis: Testing tools for Django applications. + +Automated testing is an extremely useful bug-killing tool for the modern +Web developer. You can use a collection of tests -- a **test suite** -- to +solve, or avoid, a number of problems: + + * When you're writing new code, you can use tests to validate your code + works as expected. + + * When you're refactoring or modifying old code, you can use tests to + ensure your changes haven't affected your application's behavior + unexpectedly. + +Testing a Web application is a complex task, because a Web application is made +of several layers of logic -- from HTTP-level request handling, to form +validation and processing, to template rendering. With Django's test-execution +framework and assorted utilities, you can simulate requests, insert test data, +inspect your application's output and generally verify your code is doing what +it should be doing. + +The best part is, it's really easy. + +This document is split into two primary sections. First, we explain how to +write tests with Django. Then, we explain how to run them. + +Writing tests +============= + +There are two primary ways to write tests with Django, corresponding to the +two test frameworks that ship in the Python standard library. The two +frameworks are: + + * **Doctests** -- tests that are embedded in your functions' docstrings and + are written in a way that emulates a session of the Python interactive + interpreter. For example:: + + def my_func(a_list, idx): + """ + >>> a = ['larry', 'curly', 'moe'] + >>> my_func(a, 0) + 'larry' + >>> my_func(a, 1) + 'curly' + """ + return a_list[idx] + + * **Unit tests** -- tests that are expressed as methods on a Python class + that subclasses ``unittest.TestCase``. For example:: + + import unittest + + class MyFuncTestCase(unittest.TestCase): + def testBasic(self): + a = ['larry', 'curly', 'moe'] + self.assertEquals(my_func(a, 0), 'larry') + self.assertEquals(my_func(a, 1), 'curly') + +You can choose the test framework you like, depending on which syntax you +prefer, or you can mix and match, using one framework for some of your code and +the other framework for other code. You can also use any *other* Python test +frameworks, as we'll explain in a bit. + +Writing doctests +---------------- + +Doctests use Python's standard doctest_ module, which searches your docstrings +for statements that resemble a session of the Python interactive interpreter. +A full explanation of how doctest works is out of the scope of this document; +read Python's official documentation for the details. + +.. admonition:: What's a **docstring**? + + A good explanation of docstrings (and some guidelines for using them + effectively) can be found in :pep:`257`: + + A docstring is a string literal that occurs as the first statement in + a module, function, class, or method definition. Such a docstring + becomes the ``__doc__`` special attribute of that object. + + For example, this function has a docstring that describes what it does:: + + def add_two(num): + "Return the result of adding two to the provided number." + return num + 2 + + Because tests often make great documentation, putting tests directly in + your docstrings is an effective way to document *and* test your code. + +For a given Django application, the test runner looks for doctests in two +places: + + * The ``models.py`` file. You can define module-level doctests and/or a + doctest for individual models. It's common practice to put + application-level doctests in the module docstring and model-level + doctests in the model docstrings. + + * A file called ``tests.py`` in the application directory -- i.e., the + directory that holds ``models.py``. This file is a hook for any and all + doctests you want to write that aren't necessarily related to models. + +Here is an example model doctest:: + + # models.py + + from django.db import models + + class Animal(models.Model): + """ + An animal that knows how to make noise + + # Create some animals + >>> lion = Animal.objects.create(name="lion", sound="roar") + >>> cat = Animal.objects.create(name="cat", sound="meow") + + # Make 'em speak + >>> lion.speak() + 'The lion says "roar"' + >>> cat.speak() + 'The cat says "meow"' + """ + name = models.CharField(max_length=20) + sound = models.CharField(max_length=20) + + def speak(self): + return 'The %s says "%s"' % (self.name, self.sound) + +When you :ref:`run your tests `, the test runner will find this +docstring, notice that portions of it look like an interactive Python session, +and execute those lines while checking that the results match. + +In the case of model tests, note that the test runner takes care of creating +its own test database. That is, any test that accesses a database -- by +creating and saving model instances, for example -- will not affect your +production database. However, the database is not refreshed between doctests, +so if your doctest requires a certain state you should consider flushing the +database or loading a fixture. (See the section on fixtures, below, for more +on this.) Note that to use this feature, the database user Django is connecting +as must have ``CREATE DATABASE`` rights. + +For more details about how doctest works, see the `standard library +documentation for doctest`_. + +.. _doctest: http://docs.python.org/library/doctest.html +.. _standard library documentation for doctest: doctest_ + +Writing unit tests +------------------ + +Like doctests, Django's unit tests use a standard library module: unittest_. +This module uses a different way of defining tests, taking a class-based +approach. + +As with doctests, for a given Django application, the test runner looks for +unit tests in two places: + + * The ``models.py`` file. The test runner looks for any subclass of + ``unittest.TestCase`` in this module. + + * A file called ``tests.py`` in the application directory -- i.e., the + directory that holds ``models.py``. Again, the test runner looks for any + subclass of ``unittest.TestCase`` in this module. + +This example ``unittest.TestCase`` subclass is equivalent to the example given +in the doctest section above:: + + import unittest + from myapp.models import Animal + + class AnimalTestCase(unittest.TestCase): + def setUp(self): + self.lion = Animal.objects.create(name="lion", sound="roar") + self.cat = Animal.objects.create(name="cat", sound="meow") + + def testSpeaking(self): + self.assertEquals(self.lion.speak(), 'The lion says "roar"') + self.assertEquals(self.cat.speak(), 'The cat says "meow"') + +When you :ref:`run your tests `, the default behavior of the +test utility is to find all the test cases (that is, subclasses of +``unittest.TestCase``) in ``models.py`` and ``tests.py``, automatically build a +test suite out of those test cases, and run that suite. + +There is a second way to define the test suite for a module: if you define a +function called ``suite()`` in either ``models.py`` or ``tests.py``, the +Django test runner will use that function to construct the test suite for that +module. This follows the `suggested organization`_ for unit tests. See the +Python documentation for more details on how to construct a complex test +suite. + +For more details about ``unittest``, see the `standard library unittest +documentation`_. + +.. _unittest: http://docs.python.org/library/unittest.html +.. _standard library unittest documentation: unittest_ +.. _suggested organization: http://docs.python.org/library/unittest.html#organizing-tests + +Which should I use? +------------------- + +Because Django supports both of the standard Python test frameworks, it's up to +you and your tastes to decide which one to use. You can even decide to use +*both*. + +For developers new to testing, however, this choice can seem confusing. Here, +then, are a few key differences to help you decide which approach is right for +you: + + * If you've been using Python for a while, ``doctest`` will probably feel + more "pythonic". It's designed to make writing tests as easy as possible, + so it requires no overhead of writing classes or methods. You simply put + tests in docstrings. This has the added advantage of serving as + documentation (and correct documentation, at that!). + + If you're just getting started with testing, using doctests will probably + get you started faster. + + * The ``unittest`` framework will probably feel very familiar to developers + coming from Java. ``unittest`` is inspired by Java's JUnit, so you'll + feel at home with this method if you've used JUnit or any test framework + inspired by JUnit. + + * If you need to write a bunch of tests that share similar code, then + you'll appreciate the ``unittest`` framework's organization around + classes and methods. This makes it easy to abstract common tasks into + common methods. The framework also supports explicit setup and/or cleanup + routines, which give you a high level of control over the environment + in which your test cases are run. + +Again, remember that you can use both systems side-by-side (even in the same +app). In the end, most projects will eventually end up using both. Each shines +in different circumstances. + +.. _running-tests: + +Running tests +============= + +Once you've written tests, run them using the :djadmin:`test` command of +your project's ``manage.py`` utility:: + + $ ./manage.py test + +By default, this will run every test in every application in +:setting:`INSTALLED_APPS`. If you only want to run tests for a particular +application, add the application name to the command line. For example, if your +:setting:`INSTALLED_APPS` contains ``'myproject.polls'`` and +``'myproject.animals'``, you can run the ``myproject.animals`` unit tests alone +with this command:: + + $ ./manage.py test animals + +Note that we used ``animals``, not ``myproject.animals``. + +.. versionadded:: 1.0 + You can now choose which test to run. + +You can be even *more* specific by naming an individual test case. To +run a single test case in an application (for example, the +``AnimalTestCase`` described in the "Writing unit tests" section), add +the name of the test case to the label on the command line:: + + $ ./manage.py test animals.AnimalTestCase + +And it gets even more granular than that! To run a *single* test +method inside a test case, add the name of the test method to the +label:: + + $ ./manage.py test animals.AnimalTestCase.testFluffyAnimals + +.. versionadded:: 1.2 + The ability to select individual doctests was added. + +You can use the same rules if you're using doctests. Django will use the +test label as a path to the test method or class that you want to run. +If your ``models.py`` or ``tests.py`` has a function with a doctest, or +class with a class-level doctest, you can invoke that test by appending the +name of the test method or class to the label:: + + $ ./manage.py test animals.classify + +If you want to run the doctest for a specific method in a class, add the +name of the method to the label:: + + $ ./manage.py test animals.Classifier.run + +If you're using a ``__test__`` dictionary to specify doctests for a +module, Django will use the label as a key in the ``__test__`` dictionary +for defined in ``models.py`` and ``tests.py``. + +.. versionadded:: 1.2 + You can now trigger a graceful exit from a test run by pressing ``Ctrl-C``. + +If you press ``Ctrl-C`` while the tests are running, the test runner will +wait for the currently running test to complete and then exit gracefully. +During a graceful exit the test runner will output details of any test +failures, report on how many tests were run and how many errors and failures +were encountered, and destroy any test databases as usual. Thus pressing +``Ctrl-C`` can be very useful if you forget to pass the :djadminopt:`--failfast` +option, notice that some tests are unexpectedly failing, and want to get details +on the failures without waiting for the full test run to complete. + +If you do not want to wait for the currently running test to finish, you +can press ``Ctrl-C`` a second time and the test run will halt immediately, +but not gracefully. No details of the tests run before the interruption will +be reported, and any test databases created by the run will not be destroyed. + +.. admonition:: Test with warnings enabled + + It is a good idea to run your tests with ``python -Wall manage.py + test``. This will allow you to catch any deprecation warnings that + might be in your code. Django (as well as many other libraries) use + warnings to flag when features are deprecated. It can also flag + areas in your code that are not strictly wrong, but may benefit + from a better implementation. + +Running tests outside the test runner +------------------------------------- + +If you want to run tests outside of ``./manage.py test`` -- for example, +from a shell prompt -- you will need to set up the test +environment first. Django provides a convenience method to do this:: + + >>> from django.test.utils import setup_test_environment + >>> setup_test_environment() + +This convenience method sets up the test database, and puts other +Django features into modes that allow for repeatable testing. + +The call to :meth:`~django.test.utils.setup_test_environment` is made +automatically as part of the setup of `./manage.py test`. You only +need to manually invoke this method if you're not using running your +tests via Django's test runner. + +The test database +----------------- + +Tests that require a database (namely, model tests) will not use your "real" +(production) database. Separate, blank databases are created for the tests. + +Regardless of whether the tests pass or fail, the test databases are destroyed +when all the tests have been executed. + +By default the test databases get their names by prepending ``test_`` +to the value of the :setting:`NAME` settings for the databases +defined in :setting:`DATABASES`. When using the SQLite database engine +the tests will by default use an in-memory database (i.e., the +database will be created in memory, bypassing the filesystem +entirely!). If you want to use a different database name, specify +:setting:`TEST_NAME` in the dictionary for any given database in +:setting:`DATABASES`. + +Aside from using a separate database, the test runner will otherwise +use all of the same database settings you have in your settings file: +:setting:`ENGINE`, :setting:`USER`, :setting:`HOST`, etc. The test +database is created by the user specified by ``USER``, so you'll need +to make sure that the given user account has sufficient privileges to +create a new database on the system. + +.. versionadded:: 1.0 + +For fine-grained control over the character encoding of your test +database, use the :setting:`TEST_CHARSET` option. If you're using +MySQL, you can also use the :setting:`TEST_COLLATION` option to +control the particular collation used by the test database. See the +:doc:`settings documentation ` for details of these +advanced settings. + +.. _topics-testing-masterslave: + +Testing master/slave configurations +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. versionadded:: 1.2 + +If you're testing a multiple database configuration with master/slave +replication, this strategy of creating test databases poses a problem. +When the test databases are created, there won't be any replication, +and as a result, data created on the master won't be seen on the +slave. + +To compensate for this, Django allows you to define that a database is +a *test mirror*. Consider the following (simplified) example database +configuration:: + + DATABASES = { + 'default': { + 'ENGINE': 'django.db.backends.mysql', + 'NAME': 'myproject', + 'HOST': 'dbmaster', + # ... plus some other settings + }, + 'slave': { + 'ENGINE': 'django.db.backends.mysql', + 'NAME': 'myproject', + 'HOST': 'dbslave', + 'TEST_MIRROR': 'default' + # ... plus some other settings + } + } + +In this setup, we have two database servers: ``dbmaster``, described +by the database alias ``default``, and ``dbslave`` described by the +alias ``slave``. As you might expect, ``dbslave`` has been configured +by the database administrator as a read slave of ``dbmaster``, so in +normal activity, any write to ``default`` will appear on ``slave``. + +If Django created two independent test databases, this would break any +tests that expected replication to occur. However, the ``slave`` +database has been configured as a test mirror (using the +:setting:`TEST_MIRROR` setting), indicating that under testing, +``slave`` should be treated as a mirror of ``default``. + +When the test environment is configured, a test version of ``slave`` +will *not* be created. Instead the connection to ``slave`` +will be redirected to point at ``default``. As a result, writes to +``default`` will appear on ``slave`` -- but because they are actually +the same database, not because there is data replication between the +two databases. + +.. _topics-testing-creation-dependencies: + +Controlling creation order for test databases +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. versionadded:: 1.2.4 + +By default, Django will always create the ``default`` database first. +However, no guarantees are made on the creation order of any other +databases in your test setup. + +If your database configuration requires a specific creation order, you +can specify the dependencies that exist using the +:setting:`TEST_DEPENDENCIES` setting. Consider the following +(simplified) example database configuration:: + + DATABASES = { + 'default': { + # ... db settings + 'TEST_DEPENDENCIES': ['diamonds'] + }, + 'diamonds': { + # ... db settings + }, + 'clubs': { + # ... db settings + 'TEST_DEPENDENCIES': ['diamonds'] + }, + 'spades': { + # ... db settings + 'TEST_DEPENDENCIES': ['diamonds','hearts'] + }, + 'hearts': { + # ... db settings + 'TEST_DEPENDENCIES': ['diamonds','clubs'] + } + } + +Under this configuration, the ``diamonds`` database will be created first, +as it is the only database alias without dependencies. The ``default``` and +``clubs`` alias will be created next (although the order of creation of this +pair is not guaranteed); then ``hearts``; and finally ``spades``. + +If there are any circular dependencies in the +:setting:`TEST_DEPENDENCIES` definition, an ``ImproperlyConfigured`` +exception will be raised. + +Other test conditions +--------------------- + +Regardless of the value of the :setting:`DEBUG` setting in your configuration +file, all Django tests run with :setting:`DEBUG`\=False. This is to ensure that +the observed output of your code matches what will be seen in a production +setting. + +Understanding the test output +----------------------------- + +When you run your tests, you'll see a number of messages as the test runner +prepares itself. You can control the level of detail of these messages with the +``verbosity`` option on the command line:: + + Creating test database... + Creating table myapp_animal + Creating table myapp_mineral + Loading 'initial_data' fixtures... + No fixtures found. + +This tells you that the test runner is creating a test database, as described +in the previous section. + +Once the test database has been created, Django will run your tests. +If everything goes well, you'll see something like this:: + + ---------------------------------------------------------------------- + Ran 22 tests in 0.221s + + OK + +If there are test failures, however, you'll see full details about which tests +failed:: + + ====================================================================== + FAIL: Doctest: ellington.core.throttle.models + ---------------------------------------------------------------------- + Traceback (most recent call last): + File "/dev/django/test/doctest.py", line 2153, in runTest + raise self.failureException(self.format_failure(new.getvalue())) + AssertionError: Failed doctest test for myapp.models + File "/dev/myapp/models.py", line 0, in models + + ---------------------------------------------------------------------- + File "/dev/myapp/models.py", line 14, in myapp.models + Failed example: + throttle.check("actor A", "action one", limit=2, hours=1) + Expected: + True + Got: + False + + ---------------------------------------------------------------------- + Ran 2 tests in 0.048s + + FAILED (failures=1) + +A full explanation of this error output is beyond the scope of this document, +but it's pretty intuitive. You can consult the documentation of Python's +``unittest`` library for details. + +Note that the return code for the test-runner script is the total number of +failed and erroneous tests. If all the tests pass, the return code is 0. This +feature is useful if you're using the test-runner script in a shell script and +need to test for success or failure at that level. + +Testing tools +============= + +Django provides a small set of tools that come in handy when writing tests. + +The test client +--------------- + +.. module:: django.test.client + :synopsis: Django's test client. + +The test client is a Python class that acts as a dummy Web browser, allowing +you to test your views and interact with your Django-powered application +programmatically. + +Some of the things you can do with the test client are: + + * Simulate GET and POST requests on a URL and observe the response -- + everything from low-level HTTP (result headers and status codes) to + page content. + + * Test that the correct view is executed for a given URL. + + * Test that a given request is rendered by a given Django template, with + a template context that contains certain values. + +Note that the test client is not intended to be a replacement for Twill_, +Selenium_, or other "in-browser" frameworks. Django's test client has +a different focus. In short: + + * Use Django's test client to establish that the correct view is being + called and that the view is collecting the correct context data. + + * Use in-browser frameworks such as Twill and Selenium to test *rendered* + HTML and the *behavior* of Web pages, namely JavaScript functionality. + +A comprehensive test suite should use a combination of both test types. + +.. _Twill: http://twill.idyll.org/ +.. _Selenium: http://seleniumhq.org/ + +Overview and a quick example +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To use the test client, instantiate ``django.test.client.Client`` and retrieve +Web pages:: + + >>> from django.test.client import Client + >>> c = Client() + >>> response = c.post('/login/', {'username': 'john', 'password': 'smith'}) + >>> response.status_code + 200 + >>> response = c.get('/customer/details/') + >>> response.content + '>> c.get('/login/') + + This is incorrect:: + + >>> c.get('http://www.example.com/login/') + + The test client is not capable of retrieving Web pages that are not + powered by your Django project. If you need to retrieve other Web pages, + use a Python standard library module such as urllib_ or urllib2_. + + * To resolve URLs, the test client uses whatever URLconf is pointed-to by + your :setting:`ROOT_URLCONF` setting. + + * Although the above example would work in the Python interactive + interpreter, some of the test client's functionality, notably the + template-related functionality, is only available *while tests are + running*. + + The reason for this is that Django's test runner performs a bit of black + magic in order to determine which template was loaded by a given view. + This black magic (essentially a patching of Django's template system in + memory) only happens during test running. + + * By default, the test client will disable any CSRF checks + performed by your site. + + .. versionadded:: 1.2.2 + + If, for some reason, you *want* the test client to perform CSRF + checks, you can create an instance of the test client that + enforces CSRF checks. To do this, pass in the + ``enforce_csrf_checks`` argument when you construct your + client:: + + >>> from django.test import Client + >>> csrf_client = Client(enforce_csrf_checks=True) + + +.. _urllib: http://docs.python.org/library/urllib.html +.. _urllib2: http://docs.python.org/library/urllib2.html + +Making requests +~~~~~~~~~~~~~~~ + +Use the ``django.test.client.Client`` class to make requests. It requires no +arguments at time of construction: + +.. class:: Client() + + Once you have a ``Client`` instance, you can call any of the following + methods: + + .. method:: Client.get(path, data={}, follow=False, **extra) + + + Makes a GET request on the provided ``path`` and returns a ``Response`` + object, which is documented below. + + The key-value pairs in the ``data`` dictionary are used to create a GET + data payload. For example:: + + >>> c = Client() + >>> c.get('/customers/details/', {'name': 'fred', 'age': 7}) + + ...will result in the evaluation of a GET request equivalent to:: + + /customers/details/?name=fred&age=7 + + The ``extra`` keyword arguments parameter can be used to specify + headers to be sent in the request. For example:: + + >>> c = Client() + >>> c.get('/customers/details/', {'name': 'fred', 'age': 7}, + ... HTTP_X_REQUESTED_WITH='XMLHttpRequest') + + ...will send the HTTP header ``HTTP_X_REQUESTED_WITH`` to the + details view, which is a good way to test code paths that use the + :meth:`django.http.HttpRequest.is_ajax()` method. + + .. versionadded:: 1.1 + + If you already have the GET arguments in URL-encoded form, you can + use that encoding instead of using the data argument. For example, + the previous GET request could also be posed as:: + + >>> c = Client() + >>> c.get('/customers/details/?name=fred&age=7') + + If you provide a URL with both an encoded GET data and a data argument, + the data argument will take precedence. + + If you set ``follow`` to ``True`` the client will follow any redirects + and a ``redirect_chain`` attribute will be set in the response object + containing tuples of the intermediate urls and status codes. + + If you had an url ``/redirect_me/`` that redirected to ``/next/``, that + redirected to ``/final/``, this is what you'd see:: + + >>> response = c.get('/redirect_me/', follow=True) + >>> response.redirect_chain + [(u'http://testserver/next/', 302), (u'http://testserver/final/', 302)] + + .. method:: Client.post(path, data={}, content_type=MULTIPART_CONTENT, follow=False, **extra) + + Makes a POST request on the provided ``path`` and returns a + ``Response`` object, which is documented below. + + The key-value pairs in the ``data`` dictionary are used to submit POST + data. For example:: + + >>> c = Client() + >>> c.post('/login/', {'name': 'fred', 'passwd': 'secret'}) + + ...will result in the evaluation of a POST request to this URL:: + + /login/ + + ...with this POST data:: + + name=fred&passwd=secret + + If you provide ``content_type`` (e.g., ``text/xml`` for an XML + payload), the contents of ``data`` will be sent as-is in the POST + request, using ``content_type`` in the HTTP ``Content-Type`` header. + + If you don't provide a value for ``content_type``, the values in + ``data`` will be transmitted with a content type of + ``multipart/form-data``. In this case, the key-value pairs in ``data`` + will be encoded as a multipart message and used to create the POST data + payload. + + To submit multiple values for a given key -- for example, to specify + the selections for a ``