Feature for testing projects in multiple environments

[vmagamedov]

Something like tox-travis, but with containerized environments

Prototype:

- !Image
  name: test-py{3.5,3.6}
  from: python:{3.5,3.6}-alpine
  repository: reg.local/project.{{name}}
  tasks:
  - run: pip3 install {{packages|join(" ")}}
    packages:
    - pytest==3.0.3
    - flake8==3.0.4