Good Integration Practices¶
Install package with pip¶
For development, we recommend you use
venv for virtual environments and
pip for installing your application and any dependencies,
as well as the
pytest package itself.
This ensures your code and dependencies are isolated from your system Python installation.
pyproject.toml file in the root of your repository as described in
Packaging Python Projects.
The first few lines should look like this:
[build-system] requires = ["hatchling"] build-backend = "hatchling.build" [project] name = "PACKAGENAME" version = "PACKAGEVERSION"
PACKAGEVERSION are the name and version of your package respectively.
You can then install your package in “editable” mode by running from the same directory:
pip install -e .
which lets you change your source code (both tests and application) and rerun tests at will.
Conventions for Python test discovery¶
pytest implements the following standard test discovery:
If no arguments are specified then collection starts from
testpaths(if configured) or the current directory. Alternatively, command line arguments can be used in any combination of directories, file names or node ids.
Recurse into directories, unless they match
In those directories, search for
*_test.pyfiles, imported by their test package name.
From those files, collect test items:
testprefixed test functions or methods outside of class.
testprefixed test functions or methods inside
Testprefixed test classes (without an
__init__method). Methods decorated with
@classmethodsare also considered.
For examples of how to customize your test discovery Changing standard (Python) test discovery.
Within Python modules,
pytest also discovers tests using the standard
unittest.TestCase subclassing technique.
Choosing a test layout / import rules¶
pytest supports two common test layouts:
Tests outside application code¶
Putting tests into an extra directory outside your actual application code might be useful if you have many functional tests or for other reasons want to keep tests separate from actual application code (often a good idea):
pyproject.toml src/ mypkg/ __init__.py app.py view.py tests/ test_app.py test_view.py ...
This has the following benefits:
Your tests can run against an installed version after executing
pip install ..
Your tests can run against the local copy with an editable install after executing
pip install --editable ..
[tool.pytest.ini_options] addopts = [ "--import-mode=importlib", ]
Generally, but especially if you use the default import mode
it is strongly suggested to use a
Here, your application root package resides in a sub-directory of your root,
src/mypkg/ instead of
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.
If you do not use an editable install and use the
src layout as above you need to extend the Python’s
search path for module files to execute the tests against the local copy directly. You can do it in an
ad-hoc manner by setting the
PYTHONPATH environment variable:
or in a permanent manner by using the
pythonpath configuration variable and adding the
following to your
[tool.pytest.ini_options] pythonpath = "src"
If you do not use an editable install and not use the
src layout (
mypkg directly in the root
directory) you can rely on the fact that Python by default puts the current directory in
import your package and run
python -m pytest to execute the tests against the local copy directly.
See Invoking pytest versus python -m pytest for more information about the difference between calling
python -m pytest.
Tests as part of application code¶
Inlining test directories into your application package is useful if you have direct relation between tests and application modules and want to distribute them along with your application:
pyproject.toml [src/]mypkg/ __init__.py app.py view.py tests/ __init__.py test_app.py test_view.py ...
In this scheme, it is easy to run your tests using the
pytest --pyargs mypkg
pytest will discover where
mypkg is installed and collect tests from there.
Note that this layout also works in conjunction with the
src layout mentioned in the previous section.
You can use namespace packages (PEP420) for your application
but pytest will still perform test package name discovery based on the
__init__.py files. If you use one of the
two recommended file system layouts above but leave away the
files from your directories, it should just work. From
“inlined tests”, however, you will need to use absolute imports for
getting at your application code.
append import-modes, if pytest finds a
test file while recursing into the filesystem it determines the import name
basedir: this is the first “upward” (towards the root) directory not containing an
__init__.py. If e.g. both
__init__.pyfile then the parent directory of
awill become the
sys.path.insert(0, basedir)to make the test module importable under the fully qualified import name.
import a.b.test_modulewhere the path is determined by converting path separators
/into “.” characters. This means you must follow the convention of having directory and file names map directly to the import names.
The reason for this somewhat evolved importing technique is that in larger projects multiple test modules might import from each other and thus deriving a canonical import name helps to avoid surprises such as a test module getting imported twice.
--import-mode=importlib things are less convoluted because
pytest doesn’t need to change
sys.modules, making things
much less surprising.
Choosing an import mode¶
For historical reasons, pytest defaults to the
prepend import mode
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 (src layout) would be imported as
test_view top-level modules by adding
This results in a drawback compared to the import mode
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:
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
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
pytest prepends the root of the repository to
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.
importlib import mode does not have any of the drawbacks above,
sys.path is not changed when importing test modules.
Once you are done with your work and want to make sure that your actual
package passes all tests you may want to look into tox, the
virtualenv test automation tool.
tox helps you to setup virtualenv environments with pre-defined
dependencies and then executing a pre-configured test command with
options. It will run tests against the installed package and not
against your source code checkout, helping to detect packaging
Do not run via setuptools¶
Integration with setuptools is not recommended,
i.e. you should not be using
python setup.py test or
and may stop working in the future.
This is deprecated since it depends on deprecated features of setuptools
and relies on features that break security mechanisms in pip.
For example ‘setup_requires’ and ‘tests_require’ bypass
For more information and migration instructions,
see the pytest-runner notice.
See also pypa/setuptools#1684.
setuptools intends to remove the test command.
Checking with flake8-pytest-style¶
In order to ensure that pytest is being used correctly in your project, it can be helpful to use the flake8-pytest-style flake8 plugin.
flake8-pytest-style checks for common mistakes and coding style violations in pytest code, such as incorrect use of fixtures, test function names, and markers. By using this plugin, you can catch these errors early in the development process and ensure that your pytest code is consistent and easy to maintain.
A list of the lints detected by flake8-pytest-style can be found on its PyPI page.
flake8-pytest-style is not an official pytest project. Some of the rules enforce certain style choices, such as using
@pytest.fixture, but you can configure the plugin to fit your preferred style.