test_ok1/doc/en/plugins.txt

.. _plugins:

Working with plugins and conftest files
=======================================

``pytest`` implements all aspects of configuration, collection, running and reporting by calling `well specified hooks`_.  Virtually any Python module can be registered as a plugin.  It can implement any number of hook functions (usually two or three) which all have a ``pytest_`` prefix, making hook functions easy to distinguish and find.  There are three basic location types:

* `builtin plugins`_: loaded from pytest's internal ``_pytest`` directory.
* `external plugins`_: modules discovered through `setuptools entry points`_
* `conftest.py plugins`_: modules auto-discovered in test directories

.. _`pytest/plugin`: http://bitbucket.org/pytest-dev/pytest/src/tip/pytest/plugin/
.. _`conftest.py plugins`:
.. _`conftest.py`:
.. _`localplugin`:
.. _`conftest`:

conftest.py: local per-directory plugins
----------------------------------------

local ``conftest.py`` plugins contain directory-specific hook
implementations.  Session and test running activities will
invoke all hooks defined in ``conftest.py`` files closer to the
root of the filesystem.  Example: Assume the following layout
and content of files::

    a/conftest.py:
        def pytest_runtest_setup(item):
            # called for running each test in 'a' directory
            print ("setting up", item)

    a/test_sub.py:
        def test_sub():
            pass

    test_flat.py:
        def test_flat():
            pass

Here is how you might run it::

     py.test test_flat.py   # will not show "setting up"
     py.test a/test_sub.py  # will show "setting up"

.. Note::
    If you have ``conftest.py`` files which do not reside in a
    python package directory (i.e. one containing an ``__init__.py``) then
    "import conftest" can be ambiguous because there might be other
    ``conftest.py`` files as well on your PYTHONPATH or ``sys.path``.
    It is thus good practise for projects to either put ``conftest.py``
    under a package scope or to never import anything from a
    conftest.py file.

.. _`external plugins`:
.. _`extplugins`:

Installing External Plugins / Searching
---------------------------------------

Installing a plugin happens through any usual Python installation
tool, for example::

    pip install pytest-NAME
    pip uninstall pytest-NAME

If a plugin is installed, ``pytest`` automatically finds and integrates it,
there is no need to activate it.  We have a :doc:`page listing
all 3rd party plugins and their status against the latest py.test version
<plugins_index/index>` and here is a little annotated list
for some popular plugins:

.. _`django`: https://www.djangoproject.com/

* `pytest-django <http://pypi.python.org/pypi/pytest-django>`_: write tests
  for `django`_ apps, using pytest integration.

* `pytest-twisted <http://pypi.python.org/pypi/pytest-twisted>`_: write tests
  for `twisted <http://twistedmatrix.com>`_ apps, starting a reactor and
  processing deferreds from test functions.

* `pytest-capturelog <http://pypi.python.org/pypi/pytest-capturelog>`_:
  to capture and assert about messages from the logging module

* `pytest-cov <http://pypi.python.org/pypi/pytest-cov>`_:
  coverage reporting, compatible with distributed testing

* `pytest-xdist <http://pypi.python.org/pypi/pytest-xdist>`_:
  to distribute tests to CPUs and remote hosts, to run in boxed
  mode which allows to survive segmentation faults, to run in
  looponfailing mode, automatically re-running failing tests
  on file changes, see also :ref:`xdist`

* `pytest-instafail <http://pypi.python.org/pypi/pytest-instafail>`_:
  to report failures while the test run is happening.

* `pytest-bdd <http://pypi.python.org/pypi/pytest-bdd>`_ and
  `pytest-konira <http://pypi.python.org/pypi/pytest-konira>`_
  to write tests using behaviour-driven testing.

* `pytest-timeout <http://pypi.python.org/pypi/pytest-timeout>`_:
  to timeout tests based on function marks or global definitions.

* `pytest-cache <http://pypi.python.org/pypi/pytest-cache>`_:
  to interactively re-run failing tests and help other plugins to
  store test run information across invocations.

* `pytest-pep8 <http://pypi.python.org/pypi/pytest-pep8>`_:
  a ``--pep8`` option to enable PEP8 compliance checking.

* `oejskit <http://pypi.python.org/pypi/oejskit>`_:
  a plugin to run javascript unittests in life browsers

To see a complete list of all plugins with their latest testing
status against different py.test and Python versions, please visit
`pytest-plugs <http://pytest-plugs.herokuapp.com/>`_.

You may also discover more plugins through a `pytest- pypi.python.org search`_.

.. _`available installable plugins`:
.. _`pytest- pypi.python.org search`: http://pypi.python.org/pypi?%3Aaction=search&term=pytest-&submit=search


Writing a plugin by looking at examples
---------------------------------------

.. _`setuptools`: http://pypi.python.org/pypi/setuptools

If you want to write a plugin, there are many real-life examples
you can copy from:

* a custom collection example plugin: :ref:`yaml plugin`
* around 20 `builtin plugins`_ which provide pytest's own functionality
* many `external plugins`_ providing additional features

All of these plugins implement the documented `well specified hooks`_
to extend and add functionality.

You can also :ref:`contribute your plugin to pytest-dev<submitplugin>`
once it has some happy users other than yourself.


.. _`setuptools entry points`:

Making your plugin installable by others
----------------------------------------

If you want to make your plugin externally available, you
may define a so-called entry point for your distribution so
that ``pytest`` finds your plugin module.  Entry points are
a feature that is provided by `setuptools`_. pytest looks up
the ``pytest11`` entrypoint to discover its
plugins and you can thus make your plugin available by defining
it in your setuptools-invocation:

.. sourcecode:: python

    # sample ./setup.py file
    from setuptools import setup

    setup(
        name="myproject",
        packages = ['myproject']

        # the following makes a plugin available to pytest
        entry_points = {
            'pytest11': [
                'name_of_plugin = myproject.pluginmodule',
            ]
        },
    )

If a package is installed this way, ``pytest`` will load
``myproject.pluginmodule`` as a plugin which can define
`well specified hooks`_.


.. _`pluginorder`:

Plugin discovery order at tool startup
--------------------------------------

``pytest`` loads plugin modules at tool startup in the following way:

* by loading all builtin plugins

* by loading all plugins registered through `setuptools entry points`_.

* by pre-scanning the command line for the ``-p name`` option
  and loading the specified plugin before actual command line parsing.

* by loading all :file:`conftest.py` files as inferred by the command line
  invocation:

  - if no test paths are specified use current dir as a test path
  - if exists, load ``conftest.py`` and ``test*/conftest.py`` relative
    to the directory part of the first test path.

  Note that pytest does not find ``conftest.py`` files in deeper nested
  sub directories at tool startup.  It is usually a good idea to keep
  your conftest.py file in the top level test or project root directory.

* by recursively loading all plugins specified by the
  ``pytest_plugins`` variable in ``conftest.py`` files


Requiring/Loading plugins in a test module or conftest file
-----------------------------------------------------------

You can require plugins in a test module or a conftest file like this::

    pytest_plugins = "name1", "name2",

When the test module or conftest plugin is loaded the specified plugins
will be loaded as well.  You can also use dotted path like this::

    pytest_plugins = "myapp.testsupport.myplugin"

which will import the specified module as a ``pytest`` plugin.


Accessing another plugin by name
--------------------------------

If a plugin wants to collaborate with code from
another plugin it can obtain a reference through
the plugin manager like this:

.. sourcecode:: python

    plugin = config.pluginmanager.getplugin("name_of_plugin")

If you want to look at the names of existing plugins, use
the ``--traceconfig`` option.

.. _`findpluginname`:

Finding out which plugins are active
------------------------------------

If you want to find out which plugins are active in your
environment you can type::

    py.test --traceconfig

and will get an extended test header which shows activated plugins
and their names. It will also print local plugins aka
:ref:`conftest.py <conftest>` files when they are loaded.

.. _`cmdunregister`:

Deactivating / unregistering a plugin by name
---------------------------------------------

You can prevent plugins from loading or unregister them::

    py.test -p no:NAME

This means that any subsequent try to activate/load the named
plugin will it already existing.  See :ref:`findpluginname` for
how to obtain the name of a plugin.

.. _`builtin plugins`:

pytest default plugin reference
===============================


You can find the source code for the following plugins
in the `pytest repository <http://bitbucket.org/pytest-dev/pytest/>`_.

.. autosummary::

    _pytest.assertion
    _pytest.capture
    _pytest.config
    _pytest.doctest
    _pytest.genscript
    _pytest.helpconfig
    _pytest.junitxml
    _pytest.mark
    _pytest.monkeypatch
    _pytest.nose
    _pytest.pastebin
    _pytest.pdb
    _pytest.pytester
    _pytest.python
    _pytest.recwarn
    _pytest.resultlog
    _pytest.runner
    _pytest.main
    _pytest.skipping
    _pytest.terminal
    _pytest.tmpdir
    _pytest.unittest

.. _`well specified hooks`:

pytest hook reference
=====================

Hook specification and validation
---------------------------------

``pytest`` calls hook functions to implement initialization, running,
test execution and reporting.  When ``pytest`` loads a plugin it validates
that each hook function conforms to its respective hook specification.
Each hook function name and its argument names need to match a hook
specification.  However, a hook function may accept *fewer* parameters
by simply not specifying them.  If you mistype argument names or the
hook name itself you get an error showing the available arguments.

Initialization, command line and configuration hooks
----------------------------------------------------

.. currentmodule:: _pytest.hookspec

.. autofunction:: pytest_load_initial_conftests
.. autofunction:: pytest_cmdline_preparse
.. autofunction:: pytest_cmdline_parse
.. autofunction:: pytest_namespace
.. autofunction:: pytest_addoption
.. autofunction:: pytest_cmdline_main
.. autofunction:: pytest_configure
.. autofunction:: pytest_unconfigure

Generic "runtest" hooks
-----------------------

All runtest related hooks receive a :py:class:`pytest.Item` object.

.. autofunction:: pytest_runtest_protocol
.. autofunction:: pytest_runtest_setup
.. autofunction:: pytest_runtest_call
.. autofunction:: pytest_runtest_teardown
.. autofunction:: pytest_runtest_makereport

For deeper understanding you may look at the default implementation of
these hooks in :py:mod:`_pytest.runner` and maybe also
in :py:mod:`_pytest.pdb` which interacts with :py:mod:`_pytest.capture`
and its input/output capturing in order to immediately drop
into interactive debugging when a test failure occurs.

The :py:mod:`_pytest.terminal` reported specifically uses
the reporting hook to print information about a test run.

Collection hooks
----------------

``pytest`` calls the following hooks for collecting files and directories:

.. autofunction:: pytest_ignore_collect
.. autofunction:: pytest_collect_directory
.. autofunction:: pytest_collect_file

For influencing the collection of objects in Python modules
you can use the following hook:

.. autofunction:: pytest_pycollect_makeitem
.. autofunction:: pytest_generate_tests

After collection is complete, you can modify the order of
items, delete or otherwise amend the test items:

.. autofunction:: pytest_collection_modifyitems

Reporting hooks
---------------

Session related reporting hooks:

.. autofunction:: pytest_collectstart
.. autofunction:: pytest_itemcollected
.. autofunction:: pytest_collectreport
.. autofunction:: pytest_deselected

And here is the central hook for reporting about
test execution:

.. autofunction:: pytest_runtest_logreport


Debugging/Interaction hooks
---------------------------

There are few hooks which can be used for special
reporting or interaction with exceptions:

.. autofunction:: pytest_internalerror
.. autofunction:: pytest_keyboard_interrupt
.. autofunction:: pytest_exception_interact


Declaring new hooks
------------------------

Plugins and ``conftest.py`` files may declare new hooks that can then be
implemented by other plugins in order to alter behaviour or interact with
the new plugin:

.. autofunction:: pytest_addhooks

Hooks are usually declared as do-nothing functions that contain only
documentation describing when the hook will be called and what return values
are expected.

For an example, see `newhooks.py`_ from :ref:`xdist`.

.. _`newhooks.py`: https://bitbucket.org/pytest-dev/pytest-xdist/src/52082f70e7dd04b00361091b8af906c60fd6700f/xdist/newhooks.py?at=default


Using hooks from 3rd party plugins
-------------------------------------

Using new hooks from plugins as explained above might be a little tricky
because the standard `Hook specification and validation`_ mechanism:
if you depend on a plugin that is not installed,
validation will fail and the error message will not make much sense to your users.

One approach is to defer the hook implementation to a new plugin instead of
declaring the hook functions directly in your plugin module, for example::

    # contents of myplugin.py

    class DeferPlugin(object):
        """Simple plugin to defer pytest-xdist hook functions."""

        def pytest_testnodedown(self, node, error):
            """standard xdist hook function.
            """

    def pytest_configure(config):
        if config.pluginmanager.hasplugin('xdist'):
            config.pluginmanager.register(DeferPlugin())


This has the added benefit of allowing you to conditionally install hooks
depending on which plugins are installed.

hookwrapper: executing around other hooks
-------------------------------------------------

.. currentmodule:: _pytest.core

.. versionadded:: 2.7 (experimental)

pytest plugins can implement hook wrappers which which wrap the execution
of other hook implementations.  A hook wrapper is a generator function
which yields exactly once. When pytest invokes hooks it first executes
hook wrappers and passes the same arguments as to the regular hooks.

At the yield point of the hook wrapper pytest will execute the next hook
implementations and return their result to the yield point in the form of
a :py:class:`CallOutcome` instance which encapsulates a result or
exception info.  The yield point itself will thus typically not raise
exceptions (unless there are bugs).

Here is an example definition of a hook wrapper::

    import pytest

    @pytest.mark.hookwrapper
    def pytest_pyfunc_call(pyfuncitem):
        # do whatever you want before the next hook executes
        outcome = yield
        # outcome.excinfo may be None or a (cls, val, tb) tuple
        res = outcome.get_result()  # will raise if outcome was exception
        # postprocess result

Note that hook wrappers don't return results themselves, they merely
perform tracing or other side effects around the actual hook implementations.
If the result of the underlying hook is a mutable object, they may modify
that result, however.


Reference of objects involved in hooks
======================================

.. autoclass:: _pytest.config.Config()
    :members:

.. autoclass:: _pytest.config.Parser()
    :members:

.. autoclass:: _pytest.main.Node()
    :members:

.. autoclass:: _pytest.main.Collector()
    :members:
    :show-inheritance:

.. autoclass:: _pytest.main.Item()
    :members:
    :show-inheritance:

.. autoclass:: _pytest.python.Module()
    :members:
    :show-inheritance:

.. autoclass:: _pytest.python.Class()
    :members:
    :show-inheritance:

.. autoclass:: _pytest.python.Function()
    :members:
    :show-inheritance:

.. autoclass:: _pytest.runner.CallInfo()
    :members:

.. autoclass:: _pytest.runner.TestReport()
    :members:

.. autoclass:: _pytest.core.CallOutcome()
    :members: