457 lines
15 KiB
ReStructuredText
457 lines
15 KiB
ReStructuredText
.. _plugins:
|
||
.. _`writing-plugins`:
|
||
|
||
Writing plugins
|
||
===============
|
||
|
||
It is easy to implement `local conftest plugins`_ for your own project
|
||
or `pip-installable plugins`_ that can be used throughout many projects,
|
||
including third party projects. Please refer to :ref:`using plugins` if you
|
||
only want to use but not write plugins.
|
||
|
||
A plugin contains one or multiple hook functions. :ref:`Writing hooks <writinghooks>`
|
||
explains the basics and details of how you can write a hook function yourself.
|
||
``pytest`` implements all aspects of configuration, collection, running and
|
||
reporting by calling :ref:`well specified hooks <hook-reference>` of the following plugins:
|
||
|
||
* builtin plugins: loaded from pytest's internal ``_pytest`` directory.
|
||
|
||
* :ref:`external plugins <extplugins>`: modules discovered through
|
||
`setuptools entry points`_
|
||
|
||
* `conftest.py plugins`_: modules auto-discovered in test directories
|
||
|
||
In principle, each hook call is a ``1:N`` Python function call where ``N`` is the
|
||
number of registered implementation functions for a given specification.
|
||
All specifications and implementations follow the ``pytest_`` prefix
|
||
naming convention, making them easy to distinguish and find.
|
||
|
||
.. _`pluginorder`:
|
||
|
||
Plugin discovery order at tool startup
|
||
--------------------------------------
|
||
|
||
``pytest`` loads plugin modules at tool startup in the following way:
|
||
|
||
1. by scanning the command line for the ``-p no:name`` option
|
||
and *blocking* that plugin from being loaded (even builtin plugins can
|
||
be blocked this way). This happens before normal command-line parsing.
|
||
|
||
2. by loading all builtin plugins.
|
||
|
||
3. by scanning the command line for the ``-p name`` option
|
||
and loading the specified plugin. This happens before normal command-line parsing.
|
||
|
||
4. by loading all plugins registered through `setuptools entry points`_.
|
||
|
||
5. by loading all plugins specified through the :envvar:`PYTEST_PLUGINS` environment variable.
|
||
|
||
6. by loading all "initial ":file:`conftest.py` files:
|
||
|
||
- determine the test paths: specified on the command line, otherwise in
|
||
:confval:`testpaths` if defined and running from the rootdir, otherwise the
|
||
current dir
|
||
- for each test path, load ``conftest.py`` and ``test*/conftest.py`` relative
|
||
to the directory part of the test path, if exist. Before a ``conftest.py``
|
||
file is loaded, load ``conftest.py`` files in all of its parent directories.
|
||
After a ``conftest.py`` file is loaded, recursively load all plugins specified
|
||
in its :globalvar:`pytest_plugins` variable if present.
|
||
|
||
|
||
.. _`conftest.py plugins`:
|
||
.. _`localplugin`:
|
||
.. _`local conftest plugins`:
|
||
|
||
conftest.py: local per-directory plugins
|
||
----------------------------------------
|
||
|
||
Local ``conftest.py`` plugins contain directory-specific hook
|
||
implementations. Hook Session and test running activities will
|
||
invoke all hooks defined in ``conftest.py`` files closer to the
|
||
root of the filesystem. Example of implementing the
|
||
``pytest_runtest_setup`` hook so that is called for tests in the ``a``
|
||
sub directory but not for other directories::
|
||
|
||
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::
|
||
|
||
pytest test_flat.py --capture=no # will not show "setting up"
|
||
pytest a/test_sub.py --capture=no # 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 practice for projects to either put ``conftest.py``
|
||
under a package scope or to never import anything from a
|
||
``conftest.py`` file.
|
||
|
||
See also: :ref:`pythonpath`.
|
||
|
||
.. note::
|
||
Some hooks cannot be implemented in conftest.py files which are not
|
||
:ref:`initial <pluginorder>` due to how pytest discovers plugins during
|
||
startup. See the documentation of each hook for details.
|
||
|
||
Writing your own plugin
|
||
-----------------------
|
||
|
||
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`
|
||
* builtin plugins which provide pytest's own functionality
|
||
* many :ref:`external plugins <plugin-list>` providing additional features
|
||
|
||
All of these plugins implement :ref:`hooks <hook-reference>` and/or :ref:`fixtures <fixture>`
|
||
to extend and add functionality.
|
||
|
||
.. note::
|
||
Make sure to check out the excellent
|
||
`cookiecutter-pytest-plugin <https://github.com/pytest-dev/cookiecutter-pytest-plugin>`_
|
||
project, which is a `cookiecutter template <https://github.com/audreyr/cookiecutter>`_
|
||
for authoring plugins.
|
||
|
||
The template provides an excellent starting point with a working plugin,
|
||
tests running with tox, a comprehensive README file as well as a
|
||
pre-configured entry-point.
|
||
|
||
Also consider :ref:`contributing your plugin to pytest-dev<submitplugin>`
|
||
once it has some happy users other than yourself.
|
||
|
||
|
||
.. _`setuptools entry points`:
|
||
.. _`pip-installable plugins`:
|
||
|
||
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 :std:doc:`setuptools <setuptools:index>`.
|
||
|
||
pytest looks up the ``pytest11`` entrypoint to discover its
|
||
plugins, thus you can make your plugin available by defining
|
||
it in your ``pyproject.toml`` file.
|
||
|
||
.. sourcecode:: toml
|
||
|
||
# sample ./pyproject.toml file
|
||
[build-system]
|
||
requires = ["hatchling"]
|
||
build-backend = "hatchling.build"
|
||
|
||
[project]
|
||
name = "myproject"
|
||
classifiers = [
|
||
"Framework :: Pytest",
|
||
]
|
||
|
||
[project.entry-points.pytest11]
|
||
myproject = "myproject.pluginmodule"
|
||
|
||
If a package is installed this way, ``pytest`` will load
|
||
``myproject.pluginmodule`` as a plugin which can define
|
||
:ref:`hooks <hook-reference>`. Confirm registration with ``pytest --trace-config``
|
||
|
||
.. note::
|
||
|
||
Make sure to include ``Framework :: Pytest`` in your list of
|
||
`PyPI classifiers <https://pypi.org/classifiers/>`_
|
||
to make it easy for users to find your plugin.
|
||
|
||
|
||
.. _assertion-rewriting:
|
||
|
||
Assertion Rewriting
|
||
-------------------
|
||
|
||
One of the main features of ``pytest`` is the use of plain assert
|
||
statements and the detailed introspection of expressions upon
|
||
assertion failures. This is provided by "assertion rewriting" which
|
||
modifies the parsed AST before it gets compiled to bytecode. This is
|
||
done via a :pep:`302` import hook which gets installed early on when
|
||
``pytest`` starts up and will perform this rewriting when modules get
|
||
imported. However, since we do not want to test different bytecode
|
||
from what you will run in production, this hook only rewrites test modules
|
||
themselves (as defined by the :confval:`python_files` configuration option),
|
||
and any modules which are part of plugins.
|
||
Any other imported module will not be rewritten and normal assertion behaviour
|
||
will happen.
|
||
|
||
If you have assertion helpers in other modules where you would need
|
||
assertion rewriting to be enabled you need to ask ``pytest``
|
||
explicitly to rewrite this module before it gets imported.
|
||
|
||
.. autofunction:: pytest.register_assert_rewrite
|
||
:noindex:
|
||
|
||
This is especially important when you write a pytest plugin which is
|
||
created using a package. The import hook only treats ``conftest.py``
|
||
files and any modules which are listed in the ``pytest11`` entrypoint
|
||
as plugins. As an example consider the following package::
|
||
|
||
pytest_foo/__init__.py
|
||
pytest_foo/plugin.py
|
||
pytest_foo/helper.py
|
||
|
||
With the following typical ``setup.py`` extract:
|
||
|
||
.. code-block:: python
|
||
|
||
setup(..., entry_points={"pytest11": ["foo = pytest_foo.plugin"]}, ...)
|
||
|
||
In this case only ``pytest_foo/plugin.py`` will be rewritten. If the
|
||
helper module also contains assert statements which need to be
|
||
rewritten it needs to be marked as such, before it gets imported.
|
||
This is easiest by marking it for rewriting inside the
|
||
``__init__.py`` module, which will always be imported first when a
|
||
module inside a package is imported. This way ``plugin.py`` can still
|
||
import ``helper.py`` normally. The contents of
|
||
``pytest_foo/__init__.py`` will then need to look like this:
|
||
|
||
.. code-block:: python
|
||
|
||
import pytest
|
||
|
||
pytest.register_assert_rewrite("pytest_foo.helper")
|
||
|
||
|
||
Requiring/Loading plugins in a test module or conftest file
|
||
-----------------------------------------------------------
|
||
|
||
You can require plugins in a test module or a ``conftest.py`` file using :globalvar:`pytest_plugins`:
|
||
|
||
.. code-block:: python
|
||
|
||
pytest_plugins = ["name1", "name2"]
|
||
|
||
When the test module or conftest plugin is loaded the specified plugins
|
||
will be loaded as well. Any module can be blessed as a plugin, including internal
|
||
application modules:
|
||
|
||
.. code-block:: python
|
||
|
||
pytest_plugins = "myapp.testsupport.myplugin"
|
||
|
||
:globalvar:`pytest_plugins` are processed recursively, so note that in the example above
|
||
if ``myapp.testsupport.myplugin`` also declares :globalvar:`pytest_plugins`, the contents
|
||
of the variable will also be loaded as plugins, and so on.
|
||
|
||
.. _`requiring plugins in non-root conftests`:
|
||
|
||
.. note::
|
||
Requiring plugins using :globalvar:`pytest_plugins` variable in non-root
|
||
``conftest.py`` files is deprecated.
|
||
|
||
This is important because ``conftest.py`` files implement per-directory
|
||
hook implementations, but once a plugin is imported, it will affect the
|
||
entire directory tree. In order to avoid confusion, defining
|
||
:globalvar:`pytest_plugins` in any ``conftest.py`` file which is not located in the
|
||
tests root directory is deprecated, and will raise a warning.
|
||
|
||
This mechanism makes it easy to share fixtures within applications or even
|
||
external applications without the need to create external plugins using
|
||
the ``setuptools``'s entry point technique.
|
||
|
||
Plugins imported by :globalvar:`pytest_plugins` will also automatically be marked
|
||
for assertion rewriting (see :func:`pytest.register_assert_rewrite`).
|
||
However for this to have any effect the module must not be
|
||
imported already; if it was already imported at the time the
|
||
:globalvar:`pytest_plugins` statement is processed, a warning will result and
|
||
assertions inside the plugin will not be rewritten. To fix this you
|
||
can either call :func:`pytest.register_assert_rewrite` yourself before
|
||
the module is imported, or you can arrange the code to delay the
|
||
importing until after the plugin is registered.
|
||
|
||
|
||
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.get_plugin("name_of_plugin")
|
||
|
||
If you want to look at the names of existing plugins, use
|
||
the ``--trace-config`` option.
|
||
|
||
|
||
.. _registering-markers:
|
||
|
||
Registering custom markers
|
||
--------------------------
|
||
|
||
If your plugin uses any markers, you should register them so that they appear in
|
||
pytest's help text and do not :ref:`cause spurious warnings <unknown-marks>`.
|
||
For example, the following plugin would register ``cool_marker`` and
|
||
``mark_with`` for all users:
|
||
|
||
.. code-block:: python
|
||
|
||
def pytest_configure(config):
|
||
config.addinivalue_line("markers", "cool_marker: this one is for cool tests.")
|
||
config.addinivalue_line(
|
||
"markers", "mark_with(arg, arg2): this marker takes arguments."
|
||
)
|
||
|
||
|
||
Testing plugins
|
||
---------------
|
||
|
||
pytest comes with a plugin named ``pytester`` that helps you write tests for
|
||
your plugin code. The plugin is disabled by default, so you will have to enable
|
||
it before you can use it.
|
||
|
||
You can do so by adding the following line to a ``conftest.py`` file in your
|
||
testing directory:
|
||
|
||
.. code-block:: python
|
||
|
||
# content of conftest.py
|
||
|
||
pytest_plugins = ["pytester"]
|
||
|
||
Alternatively you can invoke pytest with the ``-p pytester`` command line
|
||
option.
|
||
|
||
This will allow you to use the :py:class:`pytester <pytest.Pytester>`
|
||
fixture for testing your plugin code.
|
||
|
||
Let's demonstrate what you can do with the plugin with an example. Imagine we
|
||
developed a plugin that provides a fixture ``hello`` which yields a function
|
||
and we can invoke this function with one optional parameter. It will return a
|
||
string value of ``Hello World!`` if we do not supply a value or ``Hello
|
||
{value}!`` if we do supply a string value.
|
||
|
||
.. code-block:: python
|
||
|
||
import pytest
|
||
|
||
|
||
def pytest_addoption(parser):
|
||
group = parser.getgroup("helloworld")
|
||
group.addoption(
|
||
"--name",
|
||
action="store",
|
||
dest="name",
|
||
default="World",
|
||
help='Default "name" for hello().',
|
||
)
|
||
|
||
|
||
@pytest.fixture
|
||
def hello(request):
|
||
name = request.config.getoption("name")
|
||
|
||
def _hello(name=None):
|
||
if not name:
|
||
name = request.config.getoption("name")
|
||
return f"Hello {name}!"
|
||
|
||
return _hello
|
||
|
||
|
||
Now the ``pytester`` fixture provides a convenient API for creating temporary
|
||
``conftest.py`` files and test files. It also allows us to run the tests and
|
||
return a result object, with which we can assert the tests' outcomes.
|
||
|
||
.. code-block:: python
|
||
|
||
def test_hello(pytester):
|
||
"""Make sure that our plugin works."""
|
||
|
||
# create a temporary conftest.py file
|
||
pytester.makeconftest(
|
||
"""
|
||
import pytest
|
||
|
||
@pytest.fixture(params=[
|
||
"Brianna",
|
||
"Andreas",
|
||
"Floris",
|
||
])
|
||
def name(request):
|
||
return request.param
|
||
"""
|
||
)
|
||
|
||
# create a temporary pytest test file
|
||
pytester.makepyfile(
|
||
"""
|
||
def test_hello_default(hello):
|
||
assert hello() == "Hello World!"
|
||
|
||
def test_hello_name(hello, name):
|
||
assert hello(name) == "Hello {0}!".format(name)
|
||
"""
|
||
)
|
||
|
||
# run all tests with pytest
|
||
result = pytester.runpytest()
|
||
|
||
# check that all 4 tests passed
|
||
result.assert_outcomes(passed=4)
|
||
|
||
|
||
Additionally it is possible to copy examples to the ``pytester``'s isolated environment
|
||
before running pytest on it. This way we can abstract the tested logic to separate files,
|
||
which is especially useful for longer tests and/or longer ``conftest.py`` files.
|
||
|
||
Note that for ``pytester.copy_example`` to work we need to set `pytester_example_dir`
|
||
in our ``pytest.ini`` to tell pytest where to look for example files.
|
||
|
||
.. code-block:: ini
|
||
|
||
# content of pytest.ini
|
||
[pytest]
|
||
pytester_example_dir = .
|
||
|
||
|
||
.. code-block:: python
|
||
|
||
# content of test_example.py
|
||
|
||
|
||
def test_plugin(pytester):
|
||
pytester.copy_example("test_example.py")
|
||
pytester.runpytest("-k", "test_example")
|
||
|
||
|
||
def test_example():
|
||
pass
|
||
|
||
.. code-block:: pytest
|
||
|
||
$ pytest
|
||
=========================== test session starts ============================
|
||
platform linux -- Python 3.x.y, pytest-8.x.y, pluggy-1.x.y
|
||
rootdir: /home/sweet/project
|
||
configfile: pytest.ini
|
||
collected 2 items
|
||
|
||
test_example.py .. [100%]
|
||
|
||
============================ 2 passed in 0.12s =============================
|
||
|
||
For more information about the result object that ``runpytest()`` returns, and
|
||
the methods that it provides please check out the :py:class:`RunResult
|
||
<_pytest.pytester.RunResult>` documentation.
|