=============================================== Implementation and Customization of ``py.test`` =============================================== .. contents:: .. sectnum:: .. _`basicpicture`: Collecting and running tests / implementation remarks ====================================================== In order to customize ``py.test`` it's good to understand its basic architure (WARNING: these are not guaranteed yet to stay the way they are now!):: ___________________ | | | Collector | |___________________| / \ | Item.run() | ^ receive test Items / | /execute test Item | / ___________________/ | | | Session | |___________________| ............................. . conftest.py configuration . . cmdline options . ............................. The *Session* basically receives test *Items* from a *Collector*, and executes them via the ``Item.run()`` method. It monitors the outcome of the test and reports about failures and successes. .. _`collection process`: Collectors and the test collection process ------------------------------------------ The collecting process is iterative, i.e. the session traverses and generates a *collector tree*. Here is an example of such a tree, generated with the command ``py.test --collectonly py/xmlobj``:: By default all directories not starting with a dot are traversed, looking for ``test_*.py`` and ``*_test.py`` files. Those files are imported under their `package name`_. The Module collector looks for test functions and test classes and methods. Test functions and methods are prefixed ``test`` by default. Test classes must start with a capitalized ``Test`` prefix. .. _`collector API`: test items are collectors as well --------------------------------- To make the reporting life simple for the session object items offer a ``run()`` method as well. In fact the session distinguishes "collectors" from "items" solely by interpreting their return value. If it is a list, then we recurse into it, otherwise we consider the "test" as passed. .. _`package name`: constructing the package name for test modules ------------------------------------------------- Test modules are imported under their fully qualified name. Given a filesystem ``fspath`` it is constructed as follows: * walk the directories up to the last one that contains an ``__init__.py`` file. * perform ``sys.path.insert(0, basedir)``. * import the root package as ``root`` * determine the fully qualified name for ``fspath`` by either: * calling ``root.__pkg__.getimportname(fspath)`` if the ``__pkg__`` exists.` or * otherwise use the relative path of the module path to the base dir and turn slashes into dots and strike the trailing ``.py``. Customizing the testing process =============================== writing conftest.py files ----------------------------------- You may put conftest.py files containing project-specific configuration in your project's root directory, it's usually best to put it just into the same directory level as your topmost ``__init__.py``. In fact, ``py.test`` performs an "upwards" search starting from the directory that you specify to be tested and will lookup configuration values right-to-left. You may have options that reside e.g. in your home directory but note that project specific settings will be considered first. There is a flag that helps you debugging your conftest.py configurations:: py.test --traceconfig customizing the collecting and running process ----------------------------------------------- To introduce different test items you can create one or more ``conftest.py`` files in your project. When the collection process traverses directories and modules the default collectors will produce custom Collectors and Items if they are found in a local ``conftest.py`` file. example: perform additional ReST checks +++++++++++++++++++++++++++++++++++++++ With your custom collectors or items you can completely derive from the standard way of collecting and running tests in a localized manner. Let's look at an example. If you invoke ``py.test --collectonly py/documentation`` then you get:: ... In ``py/documentation/conftest.py`` you find the following customization:: class DocDirectory(py.test.collect.Directory): def run(self): results = super(DocDirectory, self).run() for x in self.fspath.listdir('*.txt', sort=True): results.append(x.basename) return results def join(self, name): if not name.endswith('.txt'): return super(DocDirectory, self).join(name) p = self.fspath.join(name) if p.check(file=1): return ReSTChecker(p, parent=self) Directory = DocDirectory The existence of the 'Directory' name in the ``pypy/documentation/conftest.py`` module makes the collection process defer to our custom "DocDirectory" collector. We extend the set of collected test items by ``ReSTChecker`` instances which themselves create ``ReSTSyntaxTest`` and ``LinkCheckerMaker`` items. All of this instances (need to) follow the `collector API`_. Customizing the reporting of Test Failures -------------------------------------------- XXX implement Item.repr_run and Item.repr_path for your test items Writing new assertion methods ------------------------------------- XXX __tracebackhide__, and use "print" Customizing the collection process in a module ---------------------------------------------- REPEATED WARNING: details of the collection and running process are still subject to refactorings and thus details will change. If you are customizing py.test at "Item" level then you definitely want to be subscribed to the `py-dev mailing list`_ to follow ongoing development. If you have a module where you want to take responsibility for collecting your own test Items and possibly even for executing a test then you can provide `generative tests`_ that yield callables and possibly arguments as a tuple. This is especially useful for calling application test machinery with different parameter sets but counting each of the calls as a separate tests. .. _`generative tests`: test-features.html#generative-tests The other extension possibility is about specifying a custom test ``Item`` class which is responsible for setting up and executing an underlying test. Or you can extend the collection process for a whole directory tree by putting Items in a ``conftest.py`` configuration file. The collection process dynamically consults the *chain of conftest.py* modules to determine collectors and items at ``Directory``, ``Module``, ``Class``, ``Function`` or ``Generator`` level respectively. Customizing execution of Functions ---------------------------------- - ``py.test.collect.Function`` test items control execution of a test function. ``function.run()`` will get called by the session in order to actually run a test. The method is responsible for performing proper setup/teardown ("Test Fixtures") for a Function test. - ``Function.execute(target, *args)`` methods are invoked by the default ``Function.run()`` to actually execute a python function with the given (usually empty set of) arguments. .. _`py-dev mailing list`: http://codespeak.net/mailman/listinfo/py-dev