Testing against multiple or specific Python versions on macOS using Travis

travis.yml

# This Travis configuration lets you test different Python versions on macOS,
# which isn't something that's currently supported by Travis directly
language: python

# To install, we use pip to install pyenv; this, sadly, requires the --egg flag.
# Note that we can't use the --enable-framework argument for building Python
# because that breaks on Python 2.7.1 due to the lack of libSystemStubs.a (which
# that version assumes exists).
install:
  - |
    pip install -U pip
    pip install --egg --no-binary pyenv pyenv
    export PATH=~/.pyenv/bin:$PATH
    eval "$(pyenv init -)"
    pyenv install --skip-existing $PYTHON_VERSION
    pyenv global $PYTHON_VERSION
    pyenv shell $PYTHON_VERSION
    pip install -U pip setuptools wheel py
    pip install .

# In your matrix, use the PYTHON_VERSION environment variable to control the
# Python version against which you wish to run your tests
matrix:
  include:
    - os: osx
      language: generic
      env: PYTHON_VERSION=3.6.2
    - os: osx
      language: generic
      env: PYTHON_VERSION=2.7.13
    - os: osx
      language: generic
      env: PYTHON_VERSION=2.7.1

# You'll want to set your own script here
script: python setup.py test