checkout outdated dependencies with tox

check_outdated_dependencies.sh

#!/bin/bash

set -e

outdated_dependencies=$(pip list -o)

number_of_lines="$(echo -e "$outdated_dependencies" | grep "." | wc -l)"
if (( $number_of_lines > 0 ))
then
    echo -e "$outdated_dependencies"
    exit 1
else
    exit 0
fi

tox.ini

[tox]
envlist = ...,pip-outdated

# ...

[testenv:pip-outdated]
whitelist_externals = bash
deps =
  -rrequirements.txt
commands =
  pip install -e .
  bash check_outdated_dependencies.sh