Some Issues and Questions ================================== .. note:: If you don't find an answer here, checkout the :ref:`contact channels` to get help. On naming, nosetests, licensing and magic ------------------------------------------------ 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``. 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 and you should be able to run many Django and Twisted test suites without modification. .. _features: test/features.html What's this "magic" with py.test? ++++++++++++++++++++++++++++++++++++++++++ Around 2007 (version ``0.8``) some people claimed that py.test was using too much "magic". Partly this has been fixed by removing unused, deprecated or complicated code. It is today probably one of the smallest, most universally runnable and most customizable testing frameworks for Python. However, ``py.test`` still uses many metaprogramming techniques and reading its source is thus likely not something for Python beginners. A second "magic" issue is arguably the assert statement debugging feature. When loading test modules py.test rewrites the source code of assert statements. When a rewritten assert statement fails, its error message has more information than the original. py.test also has a second assert debugging technique. When an ``assert`` statement that was missed by the rewriter fails, py.test re-interprets the expression to show intermediate values if a test fails. This second 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 turn off all assertion debugging with ``py.test --assertmode=off``. .. _`py namespaces`: index.html .. _`py/__init__.py`: http://bitbucket.org/hpk42/py-trunk/src/trunk/py/__init__.py Function arguments, parametrized tests and setup ------------------------------------------------------- .. _funcargs: test/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: test/plugin/monkeypatch.html .. _tmpdir: test/plugin/tmpdir.html .. _capture: test/plugin/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. .. _`Convention over Configuration`: http://en.wikipedia.org/wiki/Convention_over_Configuration Can I yield multiple values from a funcarg factory 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. Use the `pytest_generate_tests`_ hook to solve both issues and 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