Show independence of Rails.env and RAILS_ENV

rails_env_tester.rb

#!/usr/bin/env ruby
#

def show_env(msg=nil)
  puts msg if msg
  puts "Rails.env = #{Rails.env}"
  puts "RAILS_ENV = #{ENV['RAILS_ENV']}"
  puts ''
end

def do_fork
  child_pid = fork
  unless child_pid
    show_env("after fork, in child")
    exit!
  end
  Process.waitpid(child_pid)
end

def do_thread
  thr = Thread.new do
    show_env("after thread")
  end
  thr.join
end

show_env("top level:")
Rails.env = 'test'
show_env("after setting Rails.env:")
do_fork
do_thread

Rails.env = 'development'
ENV['RAILS_ENV'] = 'test'
show_env("top_level, after setting RAILS_ENV")
do_fork
do_thread

Rails.env = 'test'
ENV['RAILS_ENV'] = 'test'
show_env("top_level, after setting both Rails.env and RAILS_ENV")
do_fork
do_thread

exit

rails_env_tester_output.txt

$ be rails runner script/tester.rb
Running via Spring preloader in process 22624
top level:
Rails.env = development
RAILS_ENV = development

after setting Rails.env:
Rails.env = test
RAILS_ENV = development

after fork, in child
Rails.env = test
RAILS_ENV = development

after thread
Rails.env = test
RAILS_ENV = development

top_level, after setting RAILS_ENV
Rails.env = development
RAILS_ENV = test

after fork, in child
Rails.env = development
RAILS_ENV = test

after thread
Rails.env = development
RAILS_ENV = test

top_level, after setting both Rails.env and RAILS_ENV
Rails.env = test
RAILS_ENV = test

after fork, in child
Rails.env = test
RAILS_ENV = test

after thread
Rails.env = test
RAILS_ENV = test