manual stubbing

example.rb

class Game
  def get_input
    gets.chomp
  end
  
  def play
    unless get_input == "quit"
      puts "Still Going"
    end
    
    return "done"
  end
end

class GameTest < Minitest::Test
  def test_it_exits
    class Game
      def get_input
        "quit"
      end
    end
    
    assert_equal "done", Game.new.play
  end
end