I'd heard that they may have used as many as 9 power units in some capacity up to today. Some not failed, but changed anyway.
Certainly most haven't failed as such, more replaced before they do (as the engine manufacturers like, as the old saying goes that you can't analyse an engine that has blown itself to pieces). Certainly most made it back to the pit-lane under their own power.
Sadly for Honda though it appears they can't even analyse an engine that is failing even when it's still largely in one piece.
At least in the past two days they appear to have used the same core power unit, as Alonso suffered the same electrical glitches as Vandoorne yesterday,; apparently fixed this afternoon. That's about as good as the news gets. Mercedes (and supposedly Ferrari, Williams and Haas) have used one engine for the whole test. Honda have used at the very least four in that time.
Apparently they're going to struggle to fix the issues by mid-season too, as they are fundamental mechanical issues, rumoured to be vibration and heat related. McLaren keep on opening the rear of the car to allow more hot air to escape, yet they still haven't been able to run the car for more than a dozen laps.
They're looking an engine penalties by Barcelona at this rate.