I usually don't test it, I test it while playing in the tourney (eastern), and make adjustments as I go along
then, in the western, I will have all my decks tested, and ready to go
It would be nice to know it works at least somewhat before you test it in the eastern, even probably give you a chance at that, then make any necessary adjustments as you go along and before the western. The more preparation the better.
in the last tourney, I couldn't participate in eastern, I slept over...
I didn't prepare any decks...
I went into western with 3 decks I prepared 15 minutes before the tourney
I played, I adjusted, and I came out second place
and thus, I trust my instinct and theorycrafting to be able to make good untested decks