Unintentionally remapped keys on a MacBook Air (2012) One day my MacBook Air mysteriously remapped the 'U', 'I' and 'O' keys to all be the alt/option key. I've no idea what triggered this, I took it to the apple shop and it seems to stay that way when they did the hardware test. Does anyone know why this could be, and hopefully recommend a way of fixing it?
Try resetting the NVRAM and the SMC on your Mac then test those keys and see if they are still remapped.

NVRAM aka PRAM
https://support.apple.com/en-us/HT204063


  How to reset NVRAM
  
  Shut down your Mac, then turn it on and immediately press and hold
  these four keys together: Option, Command, P, and R. You can release
  the keys after about 20 seconds, during which your Mac might appear to
  restart.
  
  On Mac computers that play a startup sound, you can release the keys
  after the second startup sound. On iMac Pro, you can release the keys
  after the Apple logo appears and disappears for the second time.


SMC (System Management Controller) 
https://support.apple.com/en-us/HT201295


  How to reset the SMC on Mac notebooks
  
  First, determine whether the battery is removable. Most older Mac
  notebooks have removable batteries. Mac notebooks that have
  nonremovable batteries include MacBook Pro (Early 2009 and later), all
  models of MacBook Air, MacBook (Late 2009), and MacBook (Retina,
  12-inch, Early 2015 and later). Learn more about Mac notebook
  batteries.
  
  If the battery is nonremovable:
  
  
  Choose Apple menu > Shut Down. 
  After your Mac shuts down, press Shift-Control-Option on the left side of the built-in keyboard, then press the power button at the same
  time. Hold these keys and the power button for 10 seconds. If you have
  a MacBook Pro with Touch ID, the Touch ID button is also the power
  button.
  Release all keys.
  Press the power button again to turn on your Mac.
  
  
  If the battery is removable:
  
  
  Shut down your Mac.
  Remove the battery. If you need help removing the battery, contact
  an Apple Authorized Service Provider or Apple Retail Store.
  Press and hold the power button for 5 seconds.
  Reinstall the battery.
  Press the power button again to turn on your Mac.