Yeah, forgot about the trailer logo, well reminded.
I like to test mine too but I can't see a way of testing the brake lights if I'm on my own, other than wedging a plank between the foot pedal and seat to hold it down. It's not always easy to find something reflective to put behind the trailer so you can see it when you're in the car, so the trailer icon colour is good to know about. Be even better if it blinked red or there was an error message - you'd probably not notice it otherwise, or know it was significant unless you'd read and remembered the relevant section of the manual.