tox-virtualenv-no-download

Disable virtualenv (>=14)'s downloading behaviour when running through tox.

Wait, why?

A few goals for test suites are repeatability and speed. In modern versions of virtualenv (>=14), virtualenv will reach out to pypi to download the latest version of pip, setuptools, and wheel even when it has a perfectly good copy of the wheeled packages on disk.

A few reasons why downloading is problematic:

• Reaching out to the network is slow.
• pypi goes down quite often
• You may work in a situation where installation should not come from public pypi.
• If you don't have a network connection, virtualenv will outright fail.
• Hurts repeatability as you may suddenly get a new version of setuptools / pip
• setuptools has been unstable in the past, breaking their latest version and compatibility.

How it works

The downloading behaviour of virtualenv can be disabled either by calling virtualenv --no-download or by setting the environment variable VIRTUALENV_NO_DOWNLOAD. This tox plugin sets that environment variable during the virtualenv creation.

Usage

$ pip install tox-virtualenv-no-download
# just use tox as you usually would
$ tox ...