Hi,

First: Thanks for a great product!

I am trying to test a python package (https://github.com/pharmpy/pharmpy) on both Windows and MacOS using appveyor. Since I am using tox I could use your tox example to very easily get it to work for Windows. But for MacOS I am struggling.

1. tox couldn't be installed. I had to first separately install the tornado and nose packages.
   
2. Permission denied to simply do pip install. I had to append --user
   
3. Installed bin scripts (like tox itself) wasn't in path so I had to explicitly set the PATH
   
4. It still doesn't work. For the py36 environment it cannot find the python3.6 interpreter and for the py37 environment it cannot find pytest which should get installed by tox.

Check the 1.0.14 build here: https://ci.appveyor.com/project/pharmpy/pharmpy

Here is the appveyor.yml used for the 1.0.14 build

image:
- macos
- Visual Studio 2019

environment:
  matrix:
  - TOXENV: py36
  - TOXENV: py37
  - TOXENV: py38

build: off

install:
- sh: export PATH=/Users/appveyor/Library/Python/3.7/bin:$PATH
- sh: pip3 install tornado nose --user
- sh: pip3 install tox --user
- cmd: pip install tox

test_script:
- tox