# pytest and tox¶

It is easy to integrate pytest runs with tox. If you encounter issues, please check if they are listed as a known issue and/or use the support channels.

## Basic example¶

Assuming the following layout:

tox.ini      # see below for content
setup.py     # a classic distutils/setuptools setup.py file


and the following tox.ini content:

[tox]
envlist = py35,py36

[testenv]
deps = pytest               # PYPI package providing pytest
commands = pytest {posargs} # substitute with tox' positional arguments


you can now invoke tox in the directory where your tox.ini resides. tox will sdist-package your project, create two virtualenv environments with the python3.5 and python3.6 interpreters, respectively, and will then run the specified test command in each of them.

## Extended example: change dir before test and use per-virtualenv tempdir¶

Assuming the following layout:

tox.ini      # see below for content
setup.py     # a classic distutils/setuptools setup.py file
tests        # the directory containing tests


and the following tox.ini content:

[tox]
envlist = py35,py36
[testenv]
changedir=tests
deps=pytest
commands= pytest  --basetemp={envtmpdir}  \ # pytest tempdir setting
{posargs}                 # substitute with tox' positional arguments


you can invoke tox in the directory where your tox.ini resides. Differently than in the previous example the pytest command will be executed with a current working directory set to tests and the test run will use the per-virtualenv temporary directory.

## Using multiple CPUs for test runs¶

pytest supports distributing tests to multiple processes and hosts through the pytest-xdist plugin. Here is an example configuration to make tox use this feature:

[testenv]
deps=pytest-xdist
changedir=tests
commands= pytest --basetemp={envtmpdir}  \
--confcutdir=..         \
-n 3                    \ # use three sub processes
{posargs}


## Known Issues and limitations¶

Too long filenames. you may encounter “too long filenames” for temporarily created files in your pytest run. Try to not use the “–basetemp” parameter.

installed-versus-checkout version. pytest collects test modules on the filesystem and then tries to import them under their fully qualified name. This means that if your test files are importable from somewhere then your pytest invocation may end up importing the package from the checkout directory rather than the installed package.

This issue may be characterised by pytest test-collection error messages, in python 3.x environments, that look like:

import file mismatch:
imported module 'myproj.foo.tests.test_foo' has this __file__ attribute:
/home/myuser/repos/myproj/build/lib/myproj/foo/tests/test_foo.py
which is not the same as the test file we want to collect:
/home/myuser/repos/myproj/myproj/foo/tests/test_foo.py
HINT: remove __pycache__ / .pyc files and/or use a unique basename for your test file modules


There are a few ways to prevent this.

With installed tests (the tests packages are known to setup.py), a safe and explicit option is to give the explicit path {envsitepackagesdir}/mypkg to pytest. Alternatively, it is possible to use changedir so that checked-out files are outside the import path, then pass --pyargs mypkg to pytest.

With tests that won’t be installed, the simplest way to run them against your installed package is to avoid __init__.py files in test directories; pytest will still find and import them by adding their parent directory to sys.path but they won’t be copied to other places or be found by Python’s import system outside of pytest.