Installation and Getting Started =================================== **Compatibility**: Python 2.4-3.2, Jython, PyPy on Unix/Posix and Windows .. _`getstarted`: Installation ---------------------------------------- Installation options:: easy_install -U pytest # or pip install -U pytest To check your installation has installed the correct version:: $ py.test --version This is py.test version 2.0.0, imported from /home/hpk/p/pytest/pytest.pyc If you get an error checkout :ref:`installation issues`. .. _`simpletest`: Our first test run ---------------------------------------------------------- Let's create a first test file with a simple test function:: # content of test_sample.py def func(x): return x + 1 def test_answer(): assert func(3) == 5 That's it. You can execute the test function now:: $ py.test =========================== test session starts ============================ platform linux2 -- Python 2.6.5 -- pytest-2.0.0 collecting ... collected 1 items test_sample.py F ================================= FAILURES ================================= _______________________________ test_answer ________________________________ def test_answer(): > assert func(3) == 5 E assert 4 == 5 E + where 4 = func(3) test_sample.py:5: AssertionError ========================= 1 failed in 0.02 seconds ========================= py.test found the ``test_answer`` function by following :ref:`standard test discovery rules `, basically detecting the ``test_`` prefixes. We got a failure report because our little ``func(3)`` call did not return ``5``. The report is formatted using the :ref:`standard traceback reporting`. .. note:: You can simply use the ``assert`` statement for asserting expectations because intermediate values will be presented to you. This is arguably easier than learning all the `the JUnit legacy methods`_. However, there remains one caveat to using simple asserts: your assertion expression should better be side-effect free. Because after an assertion failed py.test will re-evaluate the expression in order to present intermediate values. You will get a nice warning and you can easily fix it: compute the value ahead of the assert and then do the assertion. Or maybe just use the assert "explicit message" syntax:: assert expr, "message" # show "message" if expr is not True .. _`the JUnit legacy methods`: http://docs.python.org/library/unittest.html#test-cases .. _`assert statement`: http://docs.python.org/reference/simple_stmts.html#the-assert-statement Asserting a certain exception is raised -------------------------------------------------------------- If you want to assert some code raises an exception you can use the ``raises`` helper:: # content of test_sysexit.py import pytest def f(): raise SystemExit(1) def test_mytest(): with pytest.raises(SystemExit): f() Running it with, this time in "quiet" reporting mode:: $ py.test -q test_sysexit.py collecting ... collected 1 items . 1 passed in 0.00 seconds .. todo:: For further ways to assert exceptions see the `raises` Grouping multiple tests in a class -------------------------------------------------------------- If you start to have more than a few tests it often makes sense to group tests logically, in classes and modules. Let's put two tests in a class like this:: # content of test_class.py class TestClass: def test_one(self): x = "this" assert 'h' in x def test_two(self): x = "hello" assert hasattr(x, 'check') The two tests are found because of the standard :ref:`test discovery`. There is no need to subclass anything. We can simply run the module by passing its filename:: $ py.test -q test_class.py collecting ... collected 2 items .F ================================= FAILURES ================================= ____________________________ TestClass.test_two ____________________________ self = def test_two(self): x = "hello" > assert hasattr(x, 'check') E assert hasattr('hello', 'check') test_class.py:8: AssertionError 1 failed, 1 passed in 0.02 seconds The first test passed, the second failed. Again we can easily see the intermediate values used in the assertion, helping us to understand the reason for the failure. Going functional: requesting a unique temporary directory -------------------------------------------------------------- For functional tests one often needs to create some files and pass them to application objects. py.test provides the versatile :ref:`funcarg mechanism` which allows to request arbitrary resources, for example a unique temporary directory:: # content of test_tmpdir.py def test_needsfiles(tmpdir): print tmpdir assert 0 We list the name ``tmpdir`` in the test function signature and py.test will lookup and call a factory to create the resource before performing the test function call. Let's just run it:: $ py.test -q test_tmpdir.py collecting ... collected 1 items F ================================= FAILURES ================================= _____________________________ test_needsfiles ______________________________ tmpdir = local('/tmp/pytest-7/test_needsfiles0') def test_needsfiles(tmpdir): print tmpdir > assert 0 E assert 0 test_tmpdir.py:3: AssertionError ----------------------------- Captured stdout ------------------------------ /tmp/pytest-7/test_needsfiles0 1 failed in 0.04 seconds Before the test runs, a unique-per-test-invocation temporary directory was created. More info at :ref:`tmpdir handling`. You can find out what kind of builtin :ref:`funcargs` exist by typing:: py.test --funcargs # shows builtin and custom function arguments where to go next ------------------------------------- Here are a few suggestions where to go next: * :ref:`cmdline` for command line invocation examples * :ref:`good practises` for virtualenv, test layout, genscript support * :ref:`apiref` for documentation and examples on using py.test * :ref:`plugins` managing and writing plugins .. _`installation issues`: Known Installation issues ------------------------------ easy_install or pip not found? ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Consult `distribute docs`_ to install the ``easy_install`` tool on your machine. You may also use the older `setuptools`_ project but it lacks bug fixes and does not work on Python3. If you use Python2 you may also install pip_. py.test not found on Windows despite installation? ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ .. _`Python for Windows`: http://www.imladris.com/Scripts/PythonForWindows.html - **Windows**: If "easy_install" or "py.test" are not found you need to add the Python script path to your ``PATH``, see here: `Python for Windows`_. You may alternatively use an `ActivePython install`_ which does this for you automatically. .. _`ActivePython install`: http://www.activestate.com/activepython/downloads .. _`Jython does not create command line launchers`: http://bugs.jython.org/issue1491 - **Jython2.5.1 on Windows XP**: `Jython does not create command line launchers`_ so ``py.test`` will not work correctly. You may install py.test on CPython and type ``py.test --genscript=mytest`` and then use ``jython mytest`` to run py.test for your tests to run in Jython. :ref:`examples` for more complex examples .. include:: links.inc