PAN: a zsh tool to switch easily with completion the tox virtualenvs and tests (demo: http://i.imgur.com/kJsJTjj.gif)

pan.zsh

# Author: Chmouel Bodujnah <chmouel@chmouel.com>
#
# Pan a zsh tool to complete virtualenv tox targets and tests launched via
# testtools
#
# Demo: http://i.imgur.com/kJsJTjj.gif
#
# When you use zsh just source the file directly and when you are inside a
# project which has been pre-built with tox targets you can start do:
#   pan <TAB>
# It will complete you with all the available tox virtualenv targets
# and activate that virtualenv no matter where you are in your project.
# 
# If you press an another tab after you specified the environement like this :
# pan py34 <TAB>
# It will run a :
# .tox/py34/bin/python -mtesttools.run discover -l 
# and give you the tests to complete and run it in that venv context.
#
# Will do a proper project in itself if it proves to be useful :)
# PS: It's tailored to OpenStack workflow but can be adapted to whatever you want.

function _testtools_tests() {
    local _gitdir _target
    _gitdir=$(git rev-parse --show-toplevel 2>/dev/null)
    _target=${_gitdir}/.tox/${1}/bin/python
    
    [[ -d ${_target} ]] && return 1
    pushd ${_gitdir} >/dev/null && \
    ${_target} -m testtools.run discover -l && \
    popd >/dev/null
}

function pan() {
    local _gitdir _target
    _gitdir=$(git rev-parse --show-toplevel 2>/dev/null)
    _target=${_gitdir}/.tox/${1}/bin
    
    [[ -d ${_target} ]] || { echo "${_target} does not exists"; return 1;}
    
    # We already did all the checking in completion
    if [[ -n $2 ]];then
        ${_target}/python -mtesttools.run ${2}
    else
        source ${_gitdir}/.tox/${1}/bin/activate
    fi
}

_pan () {
    local _gitdir targets
    _gitdir=$(git rev-parse --show-toplevel 2>/dev/null)
    [[ -z ${_gitdir} ]] && return 1
    [[ -d ${_gitdir}/.tox ]] || { return 1 ;}    
    
    targets=()
    for x in ${_gitdir}/.tox/*;do
        if [[ -d ${x} && -e ${x}/bin/activate ]];then
            targets+=(${x##*/})
        fi
    done
    [[ -z ${targets} ]] && return 1
    if (( CURRENT == 2 )); then
        compadd ${targets}
    fi
    if (( CURRENT == 3 )); then
        compadd $(_testtools_tests ${words[2]})
    fi
}
compdef _pan pan

Cool! (I am looking for completion of tox, mainly to provide the list for tox -e and found this).
Is it still maintained and/or do you plan to create a separate project for it?

Instead of using git to find the .tox dir, you can do the following:

local toxroot
toxroot=((../)#.tox(N))
if (( $#toxroot )); then
  ...
fi