Build in multi buildpack support and app.json support

[blackjid]

A few elements for context

• Heroku now supports multiple buildpacks natively. Is not necessary to use the heroku-buildpack-multi.
• As far as I understand, herokuish rely on buildpack-multi to run multiple buildpacks.
• With the new addition of the buildpack test command, is necessary to use a custom made buildpack-multi to run tests if your app needs multiple buildpacks or run tests from multiple environments.
• buildpack-multi use the .buildpack file to define runtime buildpacks, and heroku use the app.json for that. The key buildpack in the app.json is only used on app creation, but the key environment.test.buildpacks is used dynamically whenever tests run.
• Heroku execute scripts defined in the app.json scripts key if they are defined (instead of the defaults from the buidlpacks)

I would love to open the discussion on how to use herokuish to run tests leveraging the buildpacks Tespack Api, having zero-config tests that can run on cloud continuous integration services of your choice.

Some questions I have:

• Should herokuish read/parse the app.json file and:
  • use the buildpacks key to load buildpacks in the buildpack build command
  • use the environment.test.buildpacks key to load buildpacks in the buildpack test command
  • use the scripts.test and scripts.test-setup keys to excute custom commands on the buildpack test

[josegonzalez]

You can do multiple buildpacks in a few different ways:

• using the buildpacks api to inject them (heroku only)
• multi-buildpacks (the .buildpacks file)
• app.json parsing