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Revamp good practices (#10206) 

* Recommend importlib import mode for new projects
* Recommend src layout more strongly
* Switch to hatchling as the packaging tool in the example (following PyPA)
* Add explanation about the different import modes
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Philipp A 2022-09-01 12:55:41 +02:00 committed by GitHub
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3 changed files with 82 additions and 101 deletions
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1
doc/en/conf.py
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@ -393,6 +393,7 @@ intersphinx_mapping = {
"tox": ("https://tox.wiki/en/stable", None),
"virtualenv": ("https://virtualenv.pypa.io/en/stable", None),
"setuptools": ("https://setuptools.pypa.io/en/stable", None),
"packaging": ("https://packaging.python.org/en/latest", None),
}

168
doc/en/explanation/goodpractices.rst
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@ -12,41 +12,26 @@ For development, we recommend you use :mod:`venv` for virtual environments and
as well as the ``pytest`` package itself.
This ensures your code and dependencies are isolated from your system Python installation.
Next, place a ``pyproject.toml`` file in the root of your package:
Create a ``pyproject.toml`` file in the root of your repository as described in
:doc:`packaging:tutorials/packaging-projects`.
The first few lines should look like this:
.. code-block:: toml
[build-system]
requires = ["setuptools >= 42"]
build-backend = "setuptools.build_meta"
and a ``setup.cfg`` file containing your package's metadata with the following minimum content:
.. code-block:: ini
requires = ["hatchling"]
build-backend = "hatchling.build"
[metadata]
name = PACKAGENAME
[options]
packages = find:
name = "PACKAGENAME"
where ``PACKAGENAME`` is the name of your package.
.. note::
If your pip version is older than ``21.3``, you'll also need a ``setup.py`` file:
.. code-block:: python
from setuptools import setup
setup()
You can then install your package in "editable" mode by running from the same directory:
.. code-block:: bash
pip install -e .
pip install -e .
which lets you change your source code (both tests and application) and rerun tests at will.
@ -89,11 +74,11 @@ to keep tests separate from actual application code (often a good idea):
.. code-block:: text
pyproject.toml
setup.cfg
mypkg/
__init__.py
app.py
view.py
src/
mypkg/
__init__.py
app.py
view.py
tests/
test_app.py
test_view.py
@ -112,72 +97,28 @@ This has the following benefits:
See :ref:`pytest vs python -m pytest` for more information about the difference between calling ``pytest`` and
``python -m pytest``.
Note that this scheme has a drawback if you are using ``prepend`` :ref:`import mode <import-modes>`
(which is the default): your test files must have **unique names**, because
``pytest`` will import them as *top-level* modules since there are no packages
to derive a full package name from. In other words, the test files in the example above will
be imported as ``test_app`` and ``test_view`` top-level modules by adding ``tests/`` to
``sys.path``.
For new projects, we recommend to use ``importlib`` :ref:`import mode <import-modes>`
(see which-import-mode_ for a detailed explanation).
To this end, add the following to your ``pyproject.toml``:
If you need to have test modules with the same name, you might add ``__init__.py`` files to your
``tests`` folder and subfolders, changing them to packages:
.. code-block:: toml
.. code-block:: text
[tool.pytest.ini_options]
addopts = [
"--import-mode=importlib",
]
pyproject.toml
setup.cfg
mypkg/
...
tests/
__init__.py
foo/
__init__.py
test_view.py
bar/
__init__.py
test_view.py
.. _src-layout:
Now pytest will load the modules as ``tests.foo.test_view`` and ``tests.bar.test_view``, allowing
you to have modules with the same name. But now this introduces a subtle problem: in order to load
the test modules from the ``tests`` directory, pytest prepends the root of the repository to
``sys.path``, which adds the side-effect that now ``mypkg`` is also importable.
Generally, but especially if you use the default import mode ``prepend``,
it is **strongly** suggested to use a ``src`` layout.
Here, your application root package resides in a sub-directory of your root,
i.e. ``src/mypkg/`` instead of ``mypkg``.
This is problematic if you are using a tool like `tox`_ to test your package in a virtual environment,
because you want to test the *installed* version of your package, not the local code from the repository.
This layout prevents a lot of common pitfalls and has many benefits,
which are better explained in this excellent `blog post`_ by Ionel Cristian Mărieș.
.. _`src-layout`:
In this situation, it is **strongly** suggested to use a ``src`` layout where application root package resides in a
sub-directory of your root:
.. code-block:: text
pyproject.toml
setup.cfg
src/
mypkg/
__init__.py
app.py
view.py
tests/
__init__.py
foo/
__init__.py
test_view.py
bar/
__init__.py
test_view.py
This layout prevents a lot of common pitfalls and has many benefits, which are better explained in this excellent
`blog post by Ionel Cristian Mărieș <https://blog.ionelmc.ro/2014/05/25/python-packaging/#the-structure>`_.
.. note::
The ``--import-mode=importlib`` option (see :ref:`import-modes`) does not have
any of the drawbacks above because ``sys.path`` is not changed when importing
test modules, so users that run into this issue are strongly encouraged to try it.
The ``src`` directory layout is still strongly recommended however.
.. _blog post: https://blog.ionelmc.ro/2014/05/25/python-packaging/#the-structure>
Tests as part of application code
@ -190,8 +131,7 @@ want to distribute them along with your application:
.. code-block:: text
pyproject.toml
setup.cfg
mypkg/
[src/]mypkg/
__init__.py
app.py
view.py
@ -253,6 +193,56 @@ Note that this layout also works in conjunction with the ``src`` layout mentione
much less surprising.
.. _which-import-mode:
Choosing an import mode
^^^^^^^^^^^^^^^^^^^^^^^
For historical reasons, pytest defaults to the ``prepend`` :ref:`import mode <import-modes>`
instead of the ``importlib`` import mode we recommend for new projects.
The reason lies in the way the ``prepend`` mode works:
Since there are no packages to derive a full package name from,
``pytest`` will import your test files as *top-level* modules.
The test files in the first example (:ref:`src layout <src-layout>`) would be imported as
``test_app`` and ``test_view`` top-level modules by adding ``tests/`` to ``sys.path``.
This results in a drawback compared to the import mode ``importlib``:
your test files must have **unique names**.
If you need to have test modules with the same name,
as a workaround you might add ``__init__.py`` files to your ``tests`` folder and subfolders,
changing them to packages:
.. code-block:: text
pyproject.toml
mypkg/
...
tests/
__init__.py
foo/
__init__.py
test_view.py
bar/
__init__.py
test_view.py
Now pytest will load the modules as ``tests.foo.test_view`` and ``tests.bar.test_view``,
allowing you to have modules with the same name.
But now this introduces a subtle problem:
in order to load the test modules from the ``tests`` directory,
pytest prepends the root of the repository to ``sys.path``,
which adds the side-effect that now ``mypkg`` is also importable.
This is problematic if you are using a tool like tox_ to test your package in a virtual environment,
because you want to test the *installed* version of your package,
not the local code from the repository.
The ``importlib`` import mode does not have any of the drawbacks above,
because ``sys.path`` is not changed when importing test modules.
.. _`buildout`: http://www.buildout.org/en/latest/
.. _`use tox`:

14
doc/en/how-to/fixtures.rst
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@ -1766,8 +1766,6 @@ Given the tests file structure is:
::
tests/
__init__.py
conftest.py
# content of tests/conftest.py
import pytest
@ -1782,8 +1780,6 @@ Given the tests file structure is:
assert username == 'username'
subfolder/
__init__.py
conftest.py
# content of tests/subfolder/conftest.py
import pytest
@ -1792,8 +1788,8 @@ Given the tests file structure is:
def username(username):
return 'overridden-' + username
test_something.py
# content of tests/subfolder/test_something.py
test_something_else.py
# content of tests/subfolder/test_something_else.py
def test_username(username):
assert username == 'overridden-username'
@ -1809,8 +1805,6 @@ Given the tests file structure is:
::
tests/
__init__.py
conftest.py
# content of tests/conftest.py
import pytest
@ -1852,8 +1846,6 @@ Given the tests file structure is:
::
tests/
__init__.py
conftest.py
# content of tests/conftest.py
import pytest
@ -1890,8 +1882,6 @@ Given the tests file structure is:
::
tests/
__init__.py
conftest.py
# content of tests/conftest.py
import pytest