Currently (1.8.14), the Arduino IDE Serial Monitor prints Backspace (\b, 0x08) as an empty block character. Ideally, it should move the cursor back one without rubout, but IMO just doing a backspacing rubout would be an improvement anyway.

There should also be an option box (like AutoScroll & ShowTimestamp) to save the user's choice as 'serial.action_backspace' in preferences.txt, so this new behaviour is optional and persisted.

Some guidance with where to put Unit Test Sketches would be appreciated.