Indeed. But my first thought is: how many programs am I using right now on my laptop, that don't have such test coverage? and... how much (probably) undiscover

Indeed. But my first thought is: how many programs am I using right now on my laptop, that don't have such test coverage? and... how much (probably) undiscovered holes will they have? That without count, that we're living in the times of the hardware related bugs.