I used to preach using a turn and slip to check on the health of the horizon.
One very dark, but fortunately still night, I kept correcting things to the point I had to pop out and look at the horizon under the stars to find that the T&S had failed and I'd precessed all the gyros out of kilter (a technical term)
One should always remember that these things happen in real life. I'd just finished my sim training on the ATR and on my very first flight as skipper under training, the EFIS horizon sloooooooly went belly up.