mastermind_test.rb

class MastermindTest

  def test_if_I_input_i_do_I_get_game_instructions
    mastermind = Mastermind.new

    output = mastermind.process_input("i")
    assert_equal "instructions", output

    output = mastermind.process_input("p")
    assert_equal "new game string", output

    output = mastermind.process_input("RGBY")
    assert_equal "wrong code", output
  end
end

repl.rb

require_relative 'mastermind'

class RePL
  def initialize
    @mastermind = Mastermind.new
    io_loop
  end

  def io_loop
    loop do
      output = @mastermind.process_input(gets.chomp)
      break if output.nil?
      puts output
    end
    return nil
  end

end