I bet you thought they didn't play ? They did. With no line judges, Chair, ballkids, money (that I know of) or points.
But they did play:
Franky it's not the most thrilling practice "match" I've seen but Fed's style in practice is pretty relaxed (contrast with Nadal who doesn't seem to have any lower gear in him.)
Interesting (to me) : at 4:46 in (still during their warm-up) Fish rips a one-handed backhand. At 11:32 in Fed hits a far less impressive two-handed backhand.