I usually just check the deck list and play without testing, but if I'm not sure what is the best way to play the deck, I play test a bit. Like in this tournament aww's deck. In some tournaments(before I send my deck) I have not play tested my own deck at all, in these cases deck has been fairly simple for AI to play. I usually run few 10-round gauntlets against legacy decks and then against AI about 5 to 10 matches with different decks. That is if I have a time.
I build decks mostly by around some card(like in this tournament around
Bloodbraid Elf). It's not the best way to build a deck, but that's the way I like it and at least enjoy playing. In these tournaments I also want to make more competitive deck(than fun), because I think there shouldn't be too much pushover decks. It keeps things interesting and people can't just make some garbage deck and try to win with it. People tend to make more creative decks when they know that, there are going to be real challenge if they are going to win.
And I think
Natural Order should be banned, in this normal legacy at least.