535 lines
18 KiB
Plaintext
535 lines
18 KiB
Plaintext
==============================================================
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**funcargs**: advanced test fixtures and parametrization
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==============================================================
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.. contents::
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:local:
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:depth: 2
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what is a "funcarg"?
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=================================================
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A *funcarg* is the short name for "test function argument". Each python test function invocation may receive one or multiple function arguments. Function argument values can be created next to the test code or in separate test configuration files which allows test functions to remain ignorant of how its base test values are created. A test function can also be called multiple times with different sets of function arguments, allowing for arbitrary parametrization. A Funcarg parameter can be any value, a simple number or an application object.
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.. _`contact possibilities`: ../contact.html
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.. _`parametrizing tests, generalized`: http://tetamap.wordpress.com/2009/05/13/parametrizing-python-tests-generalized/
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.. _`blog post about the monkeypatch funcarg`: http://tetamap.wordpress.com/2009/03/03/monkeypatching-in-unit-tests-done-right/
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.. _`xUnit style`: xunit_setup.html
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.. _`funcarg factory`:
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.. _factory:
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funcarg factories: creating test function arguments
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==============================================================
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Test functions can specify one ore more arguments ("funcargs")
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and a test module or plugin can define factory functions that provide
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the function argument. Let's look at a simple self-contained
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example that you can put into a test module:
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.. sourcecode:: python
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# ./test_simplefactory.py
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def pytest_funcarg__myfuncarg(request):
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return 42
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def test_function(myfuncarg):
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assert myfuncarg == 17
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If you run this with ``py.test test_simplefactory.py`` you see something like this:
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.. sourcecode:: python
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=========================== test session starts ============================
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python: platform linux2 -- Python 2.6.2
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test object 1: /home/hpk/hg/py/trunk/example/funcarg/test_simplefactory.py
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test_simplefactory.py F
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================================ FAILURES ==================================
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______________________________ test_function _______________________________
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myfuncarg = 42
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def test_function(myfuncarg):
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> assert myfuncarg == 17
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E assert 42 == 17
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test_simplefactory.py:6: AssertionError
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======================== 1 failed in 0.11 seconds ==========================
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This means that the test function was called with a ``myfuncarg`` value
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of ``42`` and the assert fails accordingly. Here is how py.test
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calls the test function:
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1. py.test discovers the ``test_function`` because of the ``test_`` prefix.
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The test function needs a function argument named ``myfuncarg``.
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A matching factory function is discovered by looking for the
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name ``pytest_funcarg__myfuncarg``.
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2. ``pytest_funcarg__myfuncarg(request)`` is called and
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returns the value for ``myfuncarg``.
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3. ``test_function(42)`` call is executed.
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Note that if you misspell a function argument or want
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to use one that isn't available, you'll see an error
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with a list of available function arguments. You can
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also issue::
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py.test --funcargs test_simplefactory.py
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to see available function arguments (which you can also
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think of as "resources").
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Factory functions receive a `request object`_
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which they can use to register setup/teardown
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functions or access meta data about a test.
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.. _`request object`:
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funcarg factory request objects
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------------------------------------------
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Request objects represents a handle on a specific python test function call. A request object is passed to a funcarg factory and provides access to test configuration and context as well as some `useful caching and finalization helpers`_. Here is a list of attributes:
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``request.function``: python function object requesting the argument
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``request.cls``: class object where the test function is defined in or None.
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``request.module``: module object where the test function is defined in.
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``request.config``: access to command line opts and general config
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``request.param``: if exists was passed by a previous `metafunc.addcall`_
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.. _`useful caching and finalization helpers`:
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registering funcarg related finalizers/cleanup
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----------------------------------------------------
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.. sourcecode:: python
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def addfinalizer(func):
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""" call a finalizer function when test function finishes. """
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Calling ``request.addfinalizer()`` is useful for scheduling teardown
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functions. Here is an example for providing a ``myfile``
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object that is to be closed when the execution of a
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test function finishes.
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.. sourcecode:: python
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def pytest_funcarg__myfile(self, request):
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# ... create and open a unique per-function "myfile" object ...
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request.addfinalizer(lambda: myfile.close())
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return myfile
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managing fixtures across test modules and test runs
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----------------------------------------------------------
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.. sourcecode:: python
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def cached_setup(setup, teardown=None, scope="module", extrakey=None):
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""" cache and return result of calling setup().
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The requested argument name, the scope and the ``extrakey``
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determine the cache key. The scope also determines when
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teardown(result) will be called. valid scopes are:
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scope == 'function': when the single test function run finishes.
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scope == 'module': when tests in a different module are run
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scope == 'session': when tests of the session have run.
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"""
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Calling ``request.cached_setup()`` helps you to manage fixture
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objects across several scopes. For example, for creating a Database object
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that is to be setup only once during a test session you can use the helper
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like this:
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.. sourcecode:: python
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def pytest_funcarg__database(request):
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return request.cached_setup(
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setup=lambda: Database("..."),
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teardown=lambda val: val.close(),
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scope="session"
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)
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requesting values of other funcargs
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---------------------------------------------
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.. sourcecode:: python
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def getfuncargvalue(name):
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""" Lookup and call function argument factory for the given name.
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Each function argument is only created once per function setup.
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"""
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``request.getfuncargvalue(name)`` calls another funcarg factory function.
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You can use this function if you want to `decorate a funcarg`_, i.e.
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you want to provide the "normal" value but add something
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extra. If a factory cannot be found a ``request.Error``
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exception will be raised.
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.. _`test generators`:
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.. _`parametrizing-tests`:
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generating parametrized tests
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===========================================================
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You can parametrize multiple runs of the same test
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function by adding new test function calls with different
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function argument values. Let's look at a simple self-contained
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example:
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.. sourcecode:: python
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# ./test_example.py
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def pytest_generate_tests(metafunc):
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if "numiter" in metafunc.funcargnames:
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for i in range(10):
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metafunc.addcall(funcargs=dict(numiter=i))
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def test_func(numiter):
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assert numiter < 9
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If you run this with ``py.test test_example.py`` you'll get:
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.. sourcecode:: python
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============================= test session starts ==========================
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python: platform linux2 -- Python 2.6.2
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test object 1: /home/hpk/hg/py/trunk/test_example.py
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test_example.py .........F
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================================ FAILURES ==================================
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__________________________ test_func.test_func[9] __________________________
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numiter = 9
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def test_func(numiter):
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> assert numiter < 9
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E assert 9 < 9
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/home/hpk/hg/py/trunk/test_example.py:10: AssertionError
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Here is what happens in detail:
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1. ``pytest_generate_tests(metafunc)`` hook is called once for each test
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function. It adds ten new function calls with explicit function arguments.
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2. **execute tests**: ``test_func(numiter)`` is called ten times with
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ten different arguments.
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.. _`metafunc object`:
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test generators and metafunc objects
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-------------------------------------------
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metafunc objects are passed to the ``pytest_generate_tests`` hook.
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They help to inspect a testfunction and to generate tests
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according to test configuration or values specified
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in the class or module where a test function is defined:
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``metafunc.funcargnames``: set of required function arguments for given function
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``metafunc.function``: underlying python test function
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``metafunc.cls``: class object where the test function is defined in or None.
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``metafunc.module``: the module object where the test function is defined in.
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``metafunc.config``: access to command line opts and general config
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.. _`metafunc.addcall`:
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the ``metafunc.addcall()`` method
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-----------------------------------------------
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.. sourcecode:: python
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def addcall(funcargs={}, id=None, param=None):
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""" trigger a new test function call. """
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``funcargs`` can be a dictionary of argument names
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mapped to values - providing it is called *direct parametrization*.
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If you provide an `id`` it will be used for reporting
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and identification purposes. If you don't supply an `id`
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the stringified counter of the list of added calls will be used.
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``id`` values needs to be unique between all
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invocations for a given test function.
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``param`` if specified will be seen by any
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`funcarg factory`_ as a ``request.param`` attribute.
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Setting it is called *indirect parametrization*.
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Indirect parametrization is preferable if test values are
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expensive to setup or can only be created in certain environments.
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Test generators and thus ``addcall()`` invocations are performed
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during test collection which is separate from the actual test
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setup and test run phase. With distributed testing collection
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and test setup/run happens in different process.
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.. _`tutorial examples`:
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Tutorial Examples
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=======================================
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To see how you can implement custom paramtrization schemes,
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see e.g. `parametrizing tests, generalized`_ (blog post).
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To enable creation of test support code that can flexibly
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register setup/teardown functions see the `blog post about
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the monkeypatch funcarg`_.
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If you find issues or have further suggestions for improving
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the mechanism you are welcome to checkout `contact possibilities`_ page.
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.. _`application setup tutorial example`:
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.. _appsetup:
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application specific test setup and fixtures
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---------------------------------------------------------
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Here is a basic useful step-wise example for handling application
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specific test setup. The goal is to have one place where we have the
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glue and test support code for bootstrapping and configuring application objects and allow
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test modules and test functions to stay ignorant of involved details.
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step 1: use and implement a test/app-specific "mysetup"
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+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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Let's write a simple test function living in a test file
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``test_sample.py`` that uses a ``mysetup`` funcarg for accessing test
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specific setup.
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.. sourcecode:: python
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# ./test_sample.py
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def test_answer(mysetup):
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app = mysetup.myapp()
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answer = app.question()
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assert answer == 42
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To run this test py.test needs to find and call a factory to
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obtain the required ``mysetup`` function argument. The test
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function interacts with the provided application specific setup.
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To provide the ``mysetup`` function argument we write down
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a factory method in a `local plugin`_ by putting the
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following code into a local ``conftest.py``:
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.. sourcecode:: python
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# ./conftest.py
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from myapp import MyApp
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def pytest_funcarg__mysetup(request):
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return MySetup()
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class MySetup:
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def myapp(self):
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return MyApp()
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To run the example we represent our application by putting a pseudo MyApp object into ``myapp.py``:
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.. sourcecode:: python
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# ./myapp.py
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class MyApp:
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def question(self):
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return 6 * 9
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You can now run the test with ``py.test test_sample.py`` which will
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show this failure:
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.. sourcecode:: python
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========================= test session starts =========================
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python: platform linux2 -- Python 2.6.2
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test object 1: /home/hpk/hg/py/trunk/example/funcarg/mysetup
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test_sample.py F
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============================== FAILURES ===============================
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_____________________________ test_answer _____________________________
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mysetup = <mysetup.conftest.MySetup instance at 0xa020eac>
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def test_answer(mysetup):
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app = mysetup.myapp()
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answer = app.question()
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> assert answer == 42
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E assert 54 == 42
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test_sample.py:5: AssertionError
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====================== 1 failed in 0.11 seconds =======================
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This means that our ``mysetup`` object was successfully instantiated,
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we asked it to provide an application instance and checking
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its ``question`` method resulted in the wrong answer. If you are
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confused as to what the concrete question or answers actually mean,
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please see here_ :) Otherwise proceed to step 2.
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.. _here: http://uncyclopedia.wikia.com/wiki/The_Hitchhiker's_Guide_to_the_Galaxy
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.. _`local plugin`: customize.html#local-plugin
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.. _`tut-cmdlineoption`:
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step 2: adding a command line option
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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If you provide a "funcarg" from a plugin you can easily make methods
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depend on command line options or environment settings.
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To add a command line option we update the conftest.py of
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the previous example to add a command line option
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and to offer a new mysetup method:
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.. sourcecode:: python
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# ./conftest.py
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import py
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from myapp import MyApp
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def pytest_funcarg__mysetup(request):
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return MySetup(request)
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def pytest_addoption(parser):
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parser.addoption("--ssh", action="store", default=None,
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help="specify ssh host to run tests with")
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class MySetup:
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def __init__(self, request):
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self.config = request.config
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def myapp(self):
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return MyApp()
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def getsshconnection(self):
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host = self.config.option.ssh
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if host is None:
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py.test.skip("specify ssh host with --ssh")
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return execnet.SshGateway(host)
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Now any test function can use the ``mysetup.getsshconnection()`` method like this:
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.. sourcecode:: python
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# ./test_ssh.py
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class TestClass:
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def test_function(self, mysetup):
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conn = mysetup.getsshconnection()
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# work with conn
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Running ``py.test test_ssh.py`` without specifying a command line option will result in a skipped test_function:
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.. sourcecode:: python
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========================= test session starts =========================
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python: platform linux2 -- Python 2.6.2
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test object 1: test_ssh.py
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test_ssh.py s
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________________________ skipped test summary _________________________
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conftest.py:23: [1] Skipped: 'specify ssh host with --ssh'
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====================== 1 skipped in 0.11 seconds ======================
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Note especially how the test function could stay clear knowing about how to construct test state values or when to skip and with what message. The test function can concentrate on actual test code and test state factories can interact with execution of tests.
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If you specify a command line option like ``py.test --ssh=python.org`` the test will get un-skipped and actually execute.
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.. _`accept example`:
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example: specifying and selecting acceptance tests
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--------------------------------------------------------------
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.. sourcecode:: python
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# ./conftest.py
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def pytest_option(parser):
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group = parser.getgroup("myproject")
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group.addoption("-A", dest="acceptance", action="store_true",
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help="run (slow) acceptance tests")
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def pytest_funcarg__accept(request):
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return AcceptFuncarg(request)
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class AcceptFuncarg:
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def __init__(self, request):
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if not request.config.option.acceptance:
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py.test.skip("specify -A to run acceptance tests")
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self.tmpdir = request.config.mktemp(request.function.__name__, numbered=True)
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def run(self, cmd):
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""" called by test code to execute an acceptance test. """
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self.tmpdir.chdir()
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return py.process.cmdexec(cmd)
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and the actual test function example:
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.. sourcecode:: python
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def test_some_acceptance_aspect(accept):
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accept.tmpdir.mkdir("somesub")
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result = accept.run("ls -la")
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assert "somesub" in result
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If you run this test without specifying a command line option
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the test will get skipped with an appropriate message. Otherwise
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you can start to add convenience and test support methods
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to your AcceptFuncarg and drive running of tools or
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applications and provide ways to do assertions about
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the output.
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.. _`decorate a funcarg`:
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example: decorating a funcarg in a test module
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--------------------------------------------------------------
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For larger scale setups it's sometimes useful to decorare
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a funcarg just for a particular test module. We can
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extend the `accept example`_ by putting this in our test module:
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.. sourcecode:: python
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def pytest_funcarg__accept(request):
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# call the next factory (living in our conftest.py)
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arg = request.getfuncargvalue("accept")
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# create a special layout in our tempdir
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arg.tmpdir.mkdir("special")
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return arg
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class TestSpecialAcceptance:
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def test_sometest(self, accept):
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assert accept.tmpdir.join("special").check()
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Our module level factory will be invoked first and it can
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ask its request object to call the next factory and then
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decorate its result. This mechanism allows us to stay
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ignorant of how/where the function argument is provided -
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in our example from a `conftest plugin`_.
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sidenote: the temporary directory used here are instances of
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the `py.path.local`_ class which provides many of the os.path
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methods in a convenient way.
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.. _`py.path.local`: ../path.html#local
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.. _`conftest plugin`: customize.html#conftestplugin
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