Pantheon is a unique web host, in that you are unable to edit files or add plugins directly to the live site. The following is a list of resources for when working on a site that is hosted by Pantheon:

Installing WordPress Plugins on Pantheon:
https://pantheon.io/docs/guides/wordpress-git/plugins

Pushing Plugins (or other code changes) from Pantheon dev to the live site:
https://pantheon.io/docs/pantheon-workflow#code-moves-up-content-moves-down

Fancy Infopgraphic on the Pantheon Development Cycle:
https://pantheon.io/sites/default/files/pantheon_dev_cycle_infographic_0.pdf

The 30-second version of it all this is:

  • All code changes -- whether it's custom work by Cornershop or adding a plugin -- happen on dev
  • Content changes -- adding new posts, form submissions, image uploads, etc -- happen on live
  • "test" is typically where the two are smushed together, giving a chance to verify that everything looks okay before code and content are combined once and for all on live

If testing a feature or plugin on test and you decide to not move forward with it, remember to remove the plugin or revert back to the live version.