This is an example of using Shopify's bootboot to dual-boot an app, switching with an environment variable.
To start, run:
$ bundle install
This should create
Gemfile_next.lock files for you, but it
won't (apparently) install the
RAILS_NEXT gems, so you'll also need to run:
$ RAILS_NEXT=1 bundle install
Once both sets of gems are installed, you can run the little program in this repo under each version, with:
$ bundle exec ruby program.rb Hello! Rails is version 184.108.40.206 because RAILS_NEXT=""
And under the
$ RAILS_NEXT=1 bundle exec ruby program.rb Hello! Rails is version 5.1.7 because RAILS_NEXT="1"