Pressure Sensor

pressure_sensor.rb

class Sensor
  OFFSET_IN_MBAR = 1000

  def current_pressure
  	OFFSET_IN_MBAR + random_pressure();
  end

  private 

  def random_pressure
  	Random.rand(1200)
  end
end

class Alarm
  LOWPRESSURE_THRESHOLD = 1700
  HIGHPRESSURE_THRESHOLD = 2100

  def initialize
    @sensor = Sensor.new
    @alarm_on = false
  end

  def check
  	pressure_value = @sensor.current_pressure
    if (pressure_value < LOWPRESSURE_THRESHOLD || HIGHPRESSURE_THRESHOLD < pressure_value)
  	  @alarm_on = true
	end
  end

  def alarm_on?
    @alarm_on
  end
end 

Refactor + Test the code

• Don't change the public interface of the classes
• Try as many different approaches as you can find..