code: def set_env
        if !Object.const_defined?(:RACK_ENV)
          ENV['RACK_ENV'] ||= ENV['RAILS_ENV'] || 'development'
          Object.const_set(:RACK_ENV, ENV['RACK_ENV'])
        end
        puts "Running in #{RACK_ENV} mode" if RACK_ENV == 'development'
      end
docs: PRIVATE
   Sets the environment (RACK_ENV) based on some env variables.