I don't understand the connection between these tow files

P.68 5.3

I can understand in RSpec, we fake an output object to let it pass, but I don’t understand in the real code:

When Game is initialized, how does it know where is the output come from?

Yes, we made an instance of Output class in step_definitions, but how these two file(game.rb and codebreaker_steps.rb) connected with each other? How real code can get the information from the test code when they both not to declare require each other?

In env.rb, we indeed required the codebreaker.rb in it, thus I can understand that cucumber should be able to get in touch with the REAL code, but this should be ONE-WAY PATH, isn’t it?

And yes!, I’ve noticed these code below

When /^I start a new game$/ do
  game = Codebreaker::Game.new(output)
  game.start
end

but these code should be a part of TEST and not for the REAL, right? I’m confused :(

I’m new for this, so if I’m stupid, plz forgive, thanks for help.