Some Issues and Questions ================================== .. note:: If you don't find an answer here, you may checkout `pytest Q&A at Stackoverflow `_ or other :ref:`contact channels` to get help. On naming, nosetests, licensing and magic ------------------------------------------------ How does py.test relate to nose and unittest? +++++++++++++++++++++++++++++++++++++++++++++++++ py.test and nose_ share basic philosophy when it comes to running and writing Python tests. In fact, you can run many tests written for nose with py.test. nose_ was originally created as a clone of ``py.test`` when py.test was in the ``0.8`` release cycle. Note that starting with pytest-2.0 support for running unittest test suites is majorly improved. how does py.test relate to twisted's trial? ++++++++++++++++++++++++++++++++++++++++++++++ Since some time py.test has builtin support for supporting tests written using trial. It does not itself start a reactor, however, and does not handle Deferreds returned from a test in pytest style. If you are using trial's unittest.TestCase chances are that you can just run your tests even if you return Deferreds. In addition, there also is a dedicated `pytest-twisted `_. It substitutes the usage of Django's ``manage.py test`` and allows to use all pytest features_ most of which are not available from Django directly. .. _features: features.html What's this "magic" with py.test? (historic notes) ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Around 2007 (version ``0.8``) some people thought that py.test was using too much "magic". It had been part of the `pylib`_ which contains a lot of unreleated python library code. Around 2010 there was a major cleanup refactoring, which removed unused or deprecated code and resulted in the new ``pytest`` PyPI package which strictly contains only test-related code. This relese also brought a complete pluginification such that the core is around 300 lines of code and everything else is implemented in plugins. Thus ``pytest`` today is a small, universally runnable and customizable testing framework for Python. Note, however, that ``pytest`` uses metaprogramming techniques and reading its source is thus likely not something for Python beginners. A second "magic" issue was the assert statement debugging feature. Nowadays, py.test explicitely rewrites assert statements in test modules in order to provide more useful :ref:`assert feedback `. This completely avoids previous issues of confusing assertion-reporting. It also means, that you can use Python's ``-O`` optimization without loosing assertions in test modules. py.test contains a second mostly obsolete assert debugging technique, invoked via ``--assert=reinterpret``, activated by default on Python-2.5: When an ``assert`` statement fails, py.test re-interprets the expression part to show intermediate values. This technique suffers from a caveat that the rewriting does not: If your expression has side effects (better to avoid them anyway!) the intermediate values may not be the same, confusing the reinterpreter and obfuscating the initial error (this is also explained at the command line if it happens). You can also turn off all assertion interaction using the ``--assertmode=off`` option. .. _`py namespaces`: index.html .. _`py/__init__.py`: http://bitbucket.org/hpk42/py-trunk/src/trunk/py/__init__.py Why a ``py.test`` instead of a ``pytest`` command? ++++++++++++++++++++++++++++++++++++++++++++++++++ Some of the reasons are historic, others are practical. ``py.test`` used to be part of the ``py`` package which provided several developer utilities, all starting with ``py.``, thus providing nice TAB-completion. If you install ``pip install pycmd`` you get these tools from a separate package. These days the command line tool could be called ``pytest`` but since many people have gotten used to the old name and there is another tool named "pytest" we just decided to stick with ``py.test`` for now. Function arguments, parametrized tests and setup ------------------------------------------------------- .. _funcargs: funcargs.html Is using funcarg- versus xUnit setup a style question? +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ For simple applications and for people experienced with nose_ or unittest-style test setup using `xUnit style setup`_ probably feels natural. For larger test suites, parametrized testing or setup of complex test resources using funcargs_ may feel more natural. Moreover, funcargs are ideal for writing advanced test support code (like e.g. the monkeypatch_, the tmpdir_ or capture_ funcargs) because the support code can register setup/teardown functions in a managed class/module/function scope. .. _monkeypatch: monkeypatch.html .. _tmpdir: tmpdir.html .. _capture: capture.html .. _`why pytest_pyfuncarg__ methods?`: Why the ``pytest_funcarg__*`` name for funcarg factories? ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ We like `Convention over Configuration`_ and didn't see much point in allowing a more flexible or abstract mechanism. Moreover, it is nice to be able to search for ``pytest_funcarg__MYARG`` in source code and safely find all factory functions for the ``MYARG`` function argument. .. note:: With pytest-2.3 you can use the :ref:`@pytest.fixture` decorator to mark a function as a fixture function. .. _`Convention over Configuration`: http://en.wikipedia.org/wiki/Convention_over_Configuration Can I yield multiple values from a fixture function function? ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ There are two conceptual reasons why yielding from a factory function is not possible: * Calling factories for obtaining test function arguments is part of setting up and running a test. At that point it is not possible to add new test calls to the test collection anymore. * If multiple factories yielded values there would be no natural place to determine the combination policy - in real-world examples some combinations often should not run. However, with pytest-2.3 you can use the :ref:`@pytest.fixture` decorator and specify ``params`` so that all tests depending on the factory-created resource will run multiple times with different parameters. You can also use the `pytest_generate_tests`_ hook to implement the `parametrization scheme of your choice`_. .. _`pytest_generate_tests`: test/funcargs.html#parametrizing-tests .. _`parametrization scheme of your choice`: http://tetamap.wordpress.com/2009/05/13/parametrizing-python-tests-generalized/ py.test interaction with other packages --------------------------------------------------- Issues with py.test, multiprocess and setuptools? +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ On windows the multiprocess package will instantiate sub processes by pickling and thus implicitly re-import a lot of local modules. Unfortunately, setuptools-0.6.11 does not ``if __name__=='__main__'`` protect its generated command line script. This leads to infinite recursion when running a test that instantiates Processes. A good solution is to `install Distribute`_ as a drop-in replacement for setuptools and then re-install ``pytest``. Otherwise you could fix the script that is created by setuptools by inserting an ``if __name__ == '__main__'``. Or you can create a "pytest.py" script with this content and invoke that with the python version:: import pytest if __name__ == '__main__': pytest.main() .. _`install distribute`: http://pypi.python.org/pypi/distribute#installation-instructions .. include:: links.inc