Was that part of the test?
I've got two altimeters and two static sources. If all that lot fails I'm guessing that there's some buttons I can press on the transponder to get it to tell me flight level (I shouldn't have to guess, I should
know this), failing which I can get a radar service to read it back to me. All in all a complete failure of altimetry seems slightly unlikely and is waaaay down my list of technical failures to worry about.