General tips and tricks

Interactively passing positional arguments

If you invoke tox like this:

tox -- -x tests/

the arguments after the -- will be substituted everywhere where you specify {posargs} in your test commands, for example using pytest:

# in the testenv or testenv:NAME section of your tox.ini
commands =
    pytest {posargs}

or using nosetests:

commands =
    nosetests {posargs}

the above tox invocation will trigger the test runners to stop after the first failure and to only run a particular test file.

You can specify defaults for the positional arguments using this syntax:

commands =
    nosetests {posargs:--with-coverage}

Integrating “sphinx” documentation checks

In a testenv environment you can specify any command and thus you can easily integrate sphinx documentation integrity during a tox test run. Here is an example tox.ini configuration:

    sphinx-build -W -b html -d {envtmpdir}/doctrees .  {envtmpdir}/html

This will create a dedicated docs virtual environment and install the sphinx dependency which itself will install the sphinx-build tool which you can then use as a test command. Note that sphinx output is redirected to the virtualenv environment temporary directory to prevent sphinx from caching results between runs.

You can now call:


which will make the sphinx tests part of your test run.

Selecting one or more environments to run tests against

Using the -e ENV[,ENV2,...] option you explicitely list the environments where you want to run tests against. For example, given the previous sphinx example you may call:

tox -e docs

which will make tox only manage the docs environment and call its test commands. You may specify more than one environment like this:

tox -e py25,py26

which would run the commands of the py25 and py26 testenvironments respectively. The special value ALL selects all environments.

You can also specify an environment list in your tox.ini:

envlist = py25,py26

or override it from the command line or from the environment variable TOXENV:

export TOXENV=py25,py26 # in bash style shells

Access package artifacts between multiple tox-runs

If you have multiple projects using tox you can make use of a distshare directory where tox will copy in sdist-packages so that another tox run can find the “latest” dependency. This feature allows to test a package against an unreleased development version or even an uncommitted version on your own machine.

By default, {homedir}/.tox/distshare will be used for copying in and copying out artifacts (i.e. Python packages).

For project two to depend on the one package you use the following entry:

# example two/tox.ini
    {distshare}/one-*.zip  # install latest package from "one" project

That’s all. Tox running on project one will copy the sdist-package into the distshare directory after which a tox run on project two will grab it because deps contain an entry with the one-*.zip pattern. If there is more than one matching package the highest version will be taken. tox uses verlib to compare version strings which must be compliant with PEP 386.

If you want to use this with Jenkins, also checkout the Access package artifacts between Jenkins jobs.

basepython defaults, overriding

By default, for any pyXY test environment name the underlying “pythonX.Y” executable will be searched in your system PATH. It must exist in order to successfully create virtualenv environments. On Windows a pythonX.Y named executable will be searched in typical default locations using the C:\PythonX.Y\python.exe pattern.

For jython and pypy the respective jython and pypy-c names will be looked for.

You can override any of the default settings by defining the basepython variable in a specific test environment section, for example:


Avoiding expensive sdist

Some projects are large enough that running an sdist, followed by an install every time can be prohibitively costly. To solve this, there are two different options you can add to the tox section. First, you can simply ask tox to please not make an sdist:


If you do this, your local software package will not be installed into the virtualenv. You should probably be okay with that, or take steps to deal with it in your commands section:

commands =
    python develop

Running develop is a common enough model that it has its own option:


And a corresponding command line option --develop, which will set skipsdist to True and then perform the develop step at the place where tox normally perfoms the installation of the sdist. Specifically, it actually runs pip install -e . behind the scenes, which itself calls develop.

There is an optimization coded in to not bother re-running the command if $projectname.egg-info is newer than or setup.cfg.