316 lines
9.6 KiB
Plaintext
316 lines
9.6 KiB
Plaintext
======================================================
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**funcargs**: powerful and simple test setup
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======================================================
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In version 1.0 py.test introduces a new mechanism for setting up test
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state for use by Python test functions. It is particularly useful
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for functional and integration testing but also for unit testing.
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Using funcargs you can:
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* write self-contained, simple to read and debug test functions
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* cleanly encapsulate glue code between your app and your tests
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* do test scenario setup dependent on command line opts or environment
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The basic funcarg request/provide mechanism
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=============================================
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All you need to do from a test function or test method
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is to specify an argument for your test function:
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.. sourcecode:: python
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def test_function(myarg):
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# use myarg
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For each test function that requests the ``myarg``
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argument a matching so called funcarg provider
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will be invoked. A Funcarg provider for ``myarg``
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is written down liks this:
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.. sourcecode:: python
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def pytest_funcarg__myarg(self, request):
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# return value for myarg here
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Such a provider method can live on a test class,
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test module or on a local or global plugin.
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The method is recognized by the ``pytest_funcarg__``
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prefix and is correlated to the argument
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name which follows this prefix. Because it
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has access to the "request" object a provider
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method is a uniquely powerful place for
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containing setup up of test scenarios and
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test configuration.
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.. _`request object`:
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request objects
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------------------------
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Request objects give access to command line options,
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the underlying python function and the test running
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process. Each funcarg provider method receives a ``request`` object
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that allows interaction with the test method and test
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running process. Basic attributes::
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argname: requested argument name
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function: python function object requesting the argument
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config: access to command line opts and general config
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Request objects have a ``addfinalizer`` method that
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allows to **register a finalizer method** which is
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called after a test function has finished running.
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This is useful for tearing down or cleaning up
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test state. Here is a basic example for providing
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a ``myfile`` object that will be closed upon test
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function finish:
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.. sourcecode:: python
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def pytest_funcarg__myfile(self, request):
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# ... create and open a "myfile" object ...
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request.addfinalizer(lambda: myfile.close())
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return myfile
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If you want to **decorate a function argument** that is
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provided elsewhere you can use the ``call_next_provider``
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method to obtain the "next" value:
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.. sourcecode:: python
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def pytest_funcarg__myfile(self, request):
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myfile = request.call_next_provider()
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# do something extra
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return myfile
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This will raise a ``request.Error`` exception if there
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is no next provider left. See the `decorator example`_
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for a use of this method.
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.. _`lookup order`:
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Order of funcarg provider lookup
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----------------------------------------
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For any funcarg argument request here is the
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lookup order for provider methods:
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1. test class (if we are executing a method)
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2. test module
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3. local plugins
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4. global plugins
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Funcarg Examples
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=====================
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Example: basic application specific setup
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-----------------------------------------------------
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Here is a basic useful example for handling application
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specific setup. The goal is to have one place where
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we have the glue code for bootstrapping and configuring
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application objects and allow test modules and
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test functions to stay ignorant of involved details.
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Let's start with the using side and consider a simple
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test function living in a test file ``test_sample.py``:
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.. sourcecode:: python
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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 looks up and calls a provider to obtain the
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required "mysetup" function argument. The test function simply
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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 provider method in a `local plugin`_ by putting this
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into a local ``conftest.py``:
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.. sourcecode:: python
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from myapp import MyApp
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class ConftestPlugin:
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def pytest_funcarg__mysetup(self, 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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The ``pytest_funcarg__mysetup`` method is called to
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provide a value for the test function argument.
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To complete the example we put a pseudo MyApp object
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into ``myapp.py``:
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.. sourcecode:: python
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class MyApp:
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def question(self):
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return 6 * 9
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.. _`local plugin`: test-ext.html#local-plugin
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Example: specifying funcargs in test modules or classes
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---------------------------------------------------------
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.. sourcecode:: python
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def pytest_funcarg__mysetup(request):
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result = request.call_next_provider()
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result.extra = "..."
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return result
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You can also put such a function into a test class like this:
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.. sourcecode:: python
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class TestClass:
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def pytest_funcarg__mysetup(self, request):
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# ...
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#
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Example: command line option for providing SSH-host
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-----------------------------------------------------------
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If you provide a "funcarg" from a plugin you can
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easily make methods depend on command line options
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or environment settings. Here is a complete
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example that allows to run tests involving
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an SSH connection if an ssh host is specified:
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.. sourcecode:: python
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class ConftestPlugin:
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def pytest_addoption(self, 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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pytest_funcarg__mysetup = MySetupFuncarg
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class MySetupFuncarg:
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def __init__(self, request):
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self.request = request
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def ssh_gateway(self):
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host = self.request.config.option.ssh
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if host is None:
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py.test.skip("specify ssh host with --ssh to run this test")
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return py.execnet.SshGateway(host)
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Now any test functions can use the "mysetup.ssh_gateway()" method like this:
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.. sourcecode:: python
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class TestClass:
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def test_function(self, mysetup):
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ssh_gw = mysetup.ssh_gateway()
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# work with ssh_gw
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Running this without the command line will yield this run result::
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...
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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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class ConftestPlugin:
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def pytest_option(self, 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(self, 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.maketempdir(request.argname)
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self._old = self.tmpdir.chdir()
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request.addfinalizer(self.finalize)
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def run(self):
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return py.process.cmdexec("echo hello")
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def finalize(self):
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self._old.chdir()
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# cleanup any other resources
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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()
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assert result
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That's it! This test will get automatically skipped with
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an appropriate message if you just run ``py.test``::
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... OUTPUT of py.test on this example ...
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.. _`decorator example`:
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example: decorating/extending a funcarg in a TestClass
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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 or even
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a particular test class. We can extend the `accept example`_
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by putting this in our test class:
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.. sourcecode:: python
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class TestSpecialAcceptance:
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def pytest_funcarg__accept(self, request):
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arg = request.call_next_provider()
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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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def test_sometest(self, accept):
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assert accept.tmpdir.join("special").check()
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According to the `lookup order`_ our class-specific provider will
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be invoked first. Here, we just ask our request object to
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call the next provider and decoare its result. This simple
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mechanism allows us to stay ignorant of how/where the
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function argument is provided.
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Note that we make use here of `py.path.local`_ objects
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that provide uniform access to the local filesystem.
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.. _`py.path.local`: path.html#local
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Questions and Answers
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==================================
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Why ``pytest_funcarg__*`` methods?
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------------------------------------
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When experimenting with funcargs we also considered an explicit
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registration mechanism, i.e. calling a register method e.g. on the
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config object. But lacking a good use case for this indirection and
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flexibility we decided to go for `Convention over Configuration`_
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and allow to directly specify the provider. It has the
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positive implication that you should be able to
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"grep" for `pytest_funcarg__MYARG`` and will find all
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providing sites (usually exactly one).
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.. _`Convention over Configuration`: http://en.wikipedia.org/wiki/Convention_over_Configuration
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