Pytest and tox

This project is set up to use pytest and tox, and all tests are in the /tests-folder.


pytest is NOT compatible with Python 3.3.


Using Anaconda and tox on Windows is likely to result in a “Error: InterpreterNotFound” message and fail. If that is the case, see Working with Windows, conda, tox on how to make it work.

Test in one environment

To run tests for the current Python environment, simply invoke pytest in project root, or pass test as an option argument to setup.py.


C:\dev\mypolr> pytest
C:\dev\mypolr> python setup.py test

Multiple versions

Tests can be run for multiple python versions in separate virtualenvs using tox. Its setup is defined in the tox.ini, and will run tests in separate environments for:

  • Python 2.7
  • Python 3.4
  • Python 3.5
  • Python 3.6

These need to be created first using virtualenv or conda. (Keep reading.)

All versions

To run tests in all the Python environments, simply invoke tox in project root (after the Python environments are created).


C:\dev\mypolr> tox

Specific versions

To run on only a subset (or a single one) of the configured environments, you can use the -e ENV[,ENV,...] option.

E.g., to only run tests in environments with Python version 2.7 and 3.6:

C:\dev\mypolr>tox -e py27,py36

Read more about how to integrate tox and pytest.

Working with Windows, conda, tox


Using tox and conda (miniconda or Anaconda) is at first glance not a good match, or at least on Windows. Tox expects to work from a virtualenv and not a conda environment. However, it’s possible with a few, simple steps:

Read the tips below if you’re using conda to manage Python environments and have problems with InterpreterNotFound-errors when attempting to run tox.

To use tox and conda on Windows, the following recommendations apply:

  1. For tox to find your environments, consider to either:
    • Install environments in C:\PythonXY, where X and Y is major and minor version, respectively; or
    • Make a symlink from C:\PythonXY to your real path. E.g.: mklink /J C:\Python27 C:\Anaconda3\envs\myPy27env
  2. In the environment where you call tox: install virtualenv with conda and not with pip. This seems to work well with Anaconda.
Tips 1:

Use the --prefix, -p-option to define the location of new environments:

  • Use conda install -p C:\PythonXY python=X.Y to create an environment called PythonXY in the location C:\PythonXY. (No symlink creation is needed.)
  • Use conda install -p C:\path\to\myenv python=X.Y to create an environment called myenv in the location C:\path\to\myenv. (Symlinks should be made.)
Tips 2:
Add the --yes option to prevent conda from asking confirmation upon creating environments.
Tips 3:
If your Anaconda installation is on a different drive than C, e.g. E:\Anaconda3\, then environments will be installed in the E:\Anaconda3\envs\-directory if your current working drive is E. This allows you to create envs in the same drive as the rest of Anaconda without the need to use the --prefix option.

Fast and easy fix

The tests/tox_with_conda.py-file is a utility for making the steps above with a single call.

The ToxEnvMatcher-class can be used from Python to create environments and set up the needed symlinks, but it’s also possible to use the file from command line.

Examples of use in Python:

my_envs = join('E:\\', 'Anaconda3', 'envs')
tem = ToxEnvMatcher(my_envs)
for version in '27,34,35,36'.split(','):

Examples of use from cmd.exe:

E:\dev\mypolr\tests> tox_with_conda.py E:\Anaconda3\envs 27 34 35 36

Environment prefix (defaults to py) can be overridden with -p/–env_prefix options:

E:\dev\mypolr\tests> python tox_with_conda.py E:\Anaconda3\envs 27 34 35 36 -p Python

This will create new environments in E:\Anaconda3\envs\PythonXY instead of E:\Anaconda3\envs\pyXY

If, for some reason you need to, it’s possible to use the -b/--base option to override the default base location (C:\Python):

E:\dev\mypolr\tests> tox_with_conda.py E:\Anaconda3\envs 27 34 35 36 --base D:\Python


The tox_with_conda.py-file has been uploaded to a repository of its own on https://github.com/fauskanger/tox_with_conda and can also be installed with pip:

pip install tox_with_conda

If installed with pip, then instead of

python tox_with_conda.py ...


python -m tox_with_conda ...

Travis CI

Current build and test status:
Travis CI build and test status

The .travis.yml-file defines the Travis CI setup for this project. When new code has been pushed to the git repository, Travis CI will automatically pull the updates. Then it will build and run tests for multiple versions of Python. The process can be monitored here.


Travis continuous integration is not a replacement for running tests locally before committing changes or making pull requests.