parametrizing tests
=================================================

py.test allows to easily implement your own custom
parametrization scheme for tests.  Here we provide
some examples for inspiration and re-use.

Parametrizing test methods through per-class configuration
--------------------------------------------------------------

.. _`unittest parameterizer`: http://code.google.com/p/unittest-ext/source/browse/trunk/params.py

Here is an example ``pytest_generate_function`` function implementing a
parametrization scheme similar to Michael Foords `unittest
parameterizer`_ in a lot less code::

    # content of ./test_parametrize.py
    import pytest

    def pytest_generate_tests(metafunc):
        # called once per each test function
        for funcargs in metafunc.cls.params[metafunc.function.__name__]:
            # schedule a new test function run with applied **funcargs
            metafunc.addcall(funcargs=funcargs)

    class TestClass:
        # a map specifying multiple argument sets for a test method
        params = {
            'test_equals': [dict(a=1, b=2), dict(a=3, b=3), ],
            'test_zerodivision': [dict(a=1, b=0), dict(a=3, b=2)],
        }

        def test_equals(self, a, b):
            assert a == b

        def test_zerodivision(self, a, b):
            pytest.raises(ZeroDivisionError, "a/b")

Running it means we are two tests for each test functions, using
the respective settings::

    $ py.test -q
    collecting ... collected 4 items
    F..F
    ================================= FAILURES =================================
    _________________________ TestClass.test_equals[0] _________________________
    
    self = <test_parametrize.TestClass instance at 0x26ef2d8>, a = 1, b = 2
    
        def test_equals(self, a, b):
    >       assert a == b
    E       assert 1 == 2
    
    test_parametrize.py:17: AssertionError
    ______________________ TestClass.test_zerodivision[1] ______________________
    
    self = <test_parametrize.TestClass instance at 0x26fa758>, a = 3, b = 2
    
        def test_zerodivision(self, a, b):
    >       pytest.raises(ZeroDivisionError, "a/b")
    E       Failed: DID NOT RAISE
    
    test_parametrize.py:20: Failed
    2 failed, 2 passed in 0.03 seconds

Parametrizing test methods through a decorator
--------------------------------------------------------------

Modifying the previous example we can also allow decorators
for parametrizing test methods::

    # content of test_parametrize2.py

    import pytest

    # test support code
    def params(funcarglist):
        def wrapper(function):
            function.funcarglist = funcarglist
            return function
        return wrapper

    def pytest_generate_tests(metafunc):
        for funcargs in getattr(metafunc.function, 'funcarglist', ()):
            metafunc.addcall(funcargs=funcargs)

    # actual test code
    class TestClass:
        @params([dict(a=1, b=2), dict(a=3, b=3), ])
        def test_equals(self, a, b):
            assert a == b

        @params([dict(a=1, b=0), dict(a=3, b=2)])
        def test_zerodivision(self, a, b):
            pytest.raises(ZeroDivisionError, "a/b")

Running it gives similar results as before::

    $ py.test -q test_parametrize2.py
    collecting ... collected 4 items
    F..F
    ================================= FAILURES =================================
    _________________________ TestClass.test_equals[0] _________________________
    
    self = <test_parametrize2.TestClass instance at 0x1e5e638>, a = 1, b = 2
    
        @params([dict(a=1, b=2), dict(a=3, b=3), ])
        def test_equals(self, a, b):
    >       assert a == b
    E       assert 1 == 2
    
    test_parametrize2.py:19: AssertionError
    ______________________ TestClass.test_zerodivision[1] ______________________
    
    self = <test_parametrize2.TestClass instance at 0x1e6f560>, a = 3, b = 2
    
        @params([dict(a=1, b=0), dict(a=3, b=2)])
        def test_zerodivision(self, a, b):
    >       pytest.raises(ZeroDivisionError, "a/b")
    E       Failed: DID NOT RAISE
    
    test_parametrize2.py:23: Failed
    2 failed, 2 passed in 0.03 seconds

checking serialization between Python interpreters
--------------------------------------------------------------

Here is a stripped down real-life example of using parametrized
testing for testing serialization betwee different interpreters.
We define a ``test_basic_objects`` function which is to be run
with different sets of arguments for its three arguments::

* ``python1``: first python interpreter
* ``python2``: second python interpreter
* ``obj``: object to be dumped from first interpreter and loaded into second interpreter

.. literalinclude:: multipython.py

Running it (with Python-2.4 through to Python2.7 installed)::

   . $ py.test -q multipython.py
   collecting ... collected 75 items
   ....s....s....s....ssssss....s....s....s....ssssss....s....s....s....ssssss
   48 passed, 27 skipped in 2.74 seconds