In my experience they do expect them to work and complain the loudest. And then there's Meizu. No idea what it's like now, but ~5 years ago they meddled with the system framework enough to make my app crash. We had to buy one of those phones and I then decompiled their POS ROM to work around this madness. I had to ask myself "how on earth did this pass Google's CTS" multiple times, and the answer apparently was "it never did".