Some Issues and Questions ================================== .. note:: This FAQ is here only mostly for historic reasons. Checkout `pytest Q&A at Stackoverflow `_ for many questions and answers related to pytest and/or use :ref:`contact channels` to get help. On naming, nosetests, licensing and magic ------------------------------------------------ How does pytest relate to nose and unittest? +++++++++++++++++++++++++++++++++++++++++++++++++ ``pytest`` 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 ``pytest``. nose_ was originally created as a clone of ``pytest`` when ``pytest`` 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 pytest relate to twisted's trial? ++++++++++++++++++++++++++++++++++++++++++++++ Since some time ``pytest`` 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 `_ plugin which allows you to return deferreds from pytest-style tests, allowing the use of :ref:`fixtures` and other features. how does pytest work with Django? ++++++++++++++++++++++++++++++++++++++++++++++ In 2012, some work is going into the `pytest-django plugin `_. It substitutes the usage of Django's ``manage.py test`` and allows the use of all pytest features_ most of which are not available from Django directly. .. _features: features.html What's this "magic" with pytest? (historic notes) ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Around 2007 (version ``0.8``) some people thought that ``pytest`` was using too much "magic". It had been part of the `pylib`_ which contains a lot of unrelated 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 release 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, ``pytest`` explicitly 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 losing assertions in test modules. ``pytest`` contains a second, mostly obsolete, assert debugging technique invoked via ``--assert=reinterpret``: When an ``assert`` statement fails, ``pytest`` 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 ``--assert=plain`` option. .. _`py namespaces`: index.html .. _`py/__init__.py`: http://bitbucket.org/hpk42/py-trunk/src/trunk/py/__init__.py Why can I use both ``pytest`` and ``py.test`` commands? +++++++++++++++++++++++++++++++++++++++++++++++++++++++ pytest 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. Once ``pytest`` became a separate package, the ``py.test`` name was retained due to avoid a naming conflict with another tool. This conflict was eventually resolved, and the ``pytest`` command was therefore introduced. In future versions of pytest, we may deprecate and later remove the ``py.test`` command to avoid perpetuating the confusion. pytest fixtures, parametrized tests ------------------------------------------------------- .. _funcargs: funcargs.html Is using pytest fixtures 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 fixtures_ may feel more natural. Moreover, fixtures are ideal for writing advanced test support code (like e.g. the monkeypatch_, the tmpdir_ or capture_ fixtures) 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 .. _fixtures: fixture.html .. _`why pytest_pyfuncarg__ methods?`: .. _`Convention over Configuration`: http://en.wikipedia.org/wiki/Convention_over_Configuration Can I yield multiple values from a fixture function? ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ There are two conceptual reasons why yielding from a factory function is not possible: * 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. * 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. 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`_. See also :ref:`paramexamples` for more examples. .. _`parametrization scheme of your choice`: http://tetamap.wordpress.com/2009/05/13/parametrizing-python-tests-generalized/ pytest interaction with other packages --------------------------------------------------- Issues with pytest, 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. As of mid-2013, there shouldn't be a problem anymore when you use the standard setuptools (note that distribute has been merged back into setuptools which is now shipped directly with virtualenv). .. include:: links.inc