I usually try to remember to test the seat, but only to the extent of making sure that the seat moves in both directions. Sometimes that doesn't catch everything. On my last CW flight, I had moved the seat backwards and forwards, but it didn't show that one armrest was stuck in the up position.

When I told the crew, they immediately swung into action - they even paused the process of taking meal orders - and found me another window seat (which I said I'd prefer because it would be quieter). Only that seat was also broken - it was completely unpowered. It wasn't that aircraft's finest hour. But one crew member knew how to deal with it and manually released it into the flat position. So I had a bed to sleep on, and my original seat to go back to for breakfast when I eventually woke up.