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.
Next, place a
setup.py file in the root of your package with the following minimum content:
from setuptools import setup, find_packages setup(name="PACKAGENAME", packages=find_packages())
PACKAGENAME is the name of your package. 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.
This is similar to running
python setup.py develop or
conda develop in that it installs
your package using a symlink to your development code.
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
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):
setup.py 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 ..
If you don’t have a
setup.pyfile and are relying on the fact that Python by default puts the current directory in
sys.pathto import your package, you can execute
python -m pytestto execute the tests against the local copy directly, without using
See Invoking pytest versus python -m pytest for more information about the difference between calling
python -m pytest.
Note that this scheme has a drawback if you are using
prepend import mode
(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_view top-level modules by adding
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:
setup.py mypkg/ ... tests/ __init__.py foo/ __init__.py test_view.py bar/ __init__.py test_view.py
Now pytest will load the modules as
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.
In this situation, it is strongly suggested to use a
src layout where application root package resides in a
sub-directory of your root:
setup.py 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.
--import-mode=importlib (see Import modes) doesn’t have
any of the drawbacks above because
sys.modules are not changed when importing
test modules, so users that run
into this issue are strongly encouraged to try it and report if the new option works well for them.
src directory layout is still strongly recommended however.
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:
setup.py mypkg/ __init__.py app.py view.py test/ __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 Python3 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 on Python3.3 and above. 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.
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 and its pytest support. 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 glitches.