================================== Frequently Asked Questions ================================== .. contents:: :local: :depth: 2 On naming, nosetests, licensing and magic =========================================== Why the ``py`` naming? Why not ``pytest``? ---------------------------------------------------- This mostly has historic reasons - the aim is to get away from the somewhat questionable 'py' name at some point. These days (2010) the 'py' library almost completely comprises APIs that are used by the ``py.test`` tool. There also are some other uses, e.g. of the ``py.path.local()`` and other path implementations. So it requires some work to factor them out and do the shift. Why the ``py.test`` naming? ------------------------------------ because of TAB-completion under Bash/Shells. If you hit ``py.`` you'll get a list of available development tools that all share the ``py.`` prefix. Another motivation was to unify the package ("py.test") and tool filename. What's py.test's relation to ``nosetests``? --------------------------------------------- py.test and nose_ share basic philosophy when it comes to running Python tests. In fact, with py.test-1.1.0 it is ever easier to run many test suites that currently work with ``nosetests``. nose_ was created as a clone of ``py.test`` when py.test was in the ``0.8`` release cycle so some of the newer features_ introduced with py.test-1.0 and py.test-1.1 have no counterpart in nose_. .. _nose: http://somethingaboutorange.com/mrl/projects/nose/0.11.1/ .. _features: test/features.html .. _apipkg: http://pypi.python.org/pypi/apipkg What's this "magic" with py.test? ---------------------------------------- issues where people have used the term "magic" in the past: * `py/__init__.py`_ uses the apipkg_ mechanism for lazy-importing and full control on what API you get when importing "import py". * when an ``assert`` statement fails, py.test re-interprets the expression to show intermediate values if a test fails. If your expression has side effects the intermediate values may not be the same, obfuscating the initial error (this is also explained at the command line if it happens). ``py.test --no-assert`` turns off assert re-intepretation. Sidenote: it is good practise to avoid asserts with side effects. .. _`py namespaces`: index.html .. _`py/__init__.py`: http://bitbucket.org/hpk42/py-trunk/src/trunk/py/__init__.py Where does my ``py.test`` come/import from? ---------------------------------------------- You can issue:: py.test --version which tells you both version and import location of the tool. function arguments, parametrized tests and setup ==================================================== .. _funcargs: test/funcargs.html Is using funcarg- versus xUnit-based setup a style question? --------------------------------------------------------------- It depends. For simple applications or for people experienced with nose_ or unittest-style test setup using `xUnit style setup`_ make some sense. For larger test suites, parametrized testing or setup of complex test resources using funcargs_ is recommended. 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 .. _`xUnit style setup`: test/xunit_setup.html .. _`pytest_nose`: test/plugin/nose.html .. _`why pytest_pyfuncarg__ methods?`: Why the ``pytest_funcarg__*`` name for funcarg factories? --------------------------------------------------------------- When experimenting with funcargs an explicit registration mechanism was considered. But lacking a good use case for this indirection and flexibility we decided to go for `Convention over Configuration`_ and allow to directly specify the factory. Besides removing the need for an indirection it allows to "grep" for ``pytest_funcarg__MYARG`` and will safely find all factory functions for the ``MYARG`` function argument. It helps to alleviate the de-coupling of function argument usage and creation. .. _`Convention over Configuration`: http://en.wikipedia.org/wiki/Convention_over_Configuration Can I yield multiple values from a 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 implicitely re-import a lot of local modules. Unfortuantely, 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. There are these workarounds: * `install Distribute`_ as a drop-in replacement for setuptools and install py.test * `directly use a checkout`_ which avoids all setuptools/Distribute installation If those options are not available to you, you may also manually 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 py if __name__ == '__main__': py.cmdline.pytest() .. _`directly use a checkout`: install.html#directly-use-a-checkout .. _`install distribute`: http://pypi.python.org/pypi/distribute#installation-instructions