old_contents: from gpiozero.pins.mock import MockFactory
  from gpiozero import Device, Button, LED
  from time import sleep
  
  # Set the default pin factory to a mock factory
  Device.pin_factory = MockFactory()
  
  # Construct a couple of devices attached to mock pins 16 and 17, and link the
  # devices
  led = LED(17)
  btn = Button(16)
  led.source = btn.values
  
  # Here the button isn't "pushed" so the LED's value should be False
  print(led.value)
  
  # Get a reference to mock pin 16 (used by the button)
  btn_pin = Device.pin_factory.pin(16)
  
  # Drive the pin low (this is what would happen eletrically when the button is
  # pushed)
  btn_pin.drive_low()
  sleep(0.1) # give source some time to re-read the button state
  print(led.value)
  
  btn_pin.drive_high()
  sleep(0.1)
  print(led.value)
  
new_contents: from gpiozero.pins.mock import MockFactory
  from gpiozero import Device, Button, LED
  from time import sleep
  
  # Set the default pin factory to a mock factory
  Device.pin_factory = MockFactory()
  
  # Construct a couple of devices attached to mock pins 16 and 17, and link the
  # devices
  led = LED(17)
  btn = Button(16)
  led.source = btn.values
  
  # Here the button isn't "pushed" so the LED's value should be False
  print(led.value)
  
  # Get a reference to mock pin 16 (used by the button)
  btn_pin = Device.pin_factory.pin(16)
  
  # Drive the pin low (this is what would happen electrically when the button is
  # pushed)
  btn_pin.drive_low()
  sleep(0.1) # give source some time to re-read the button state
  print(led.value)
  
  btn_pin.drive_high()
  sleep(0.1)
  print(led.value)
  
subject: Fix minor typo in mock_demo.py example