What is a quick way to test or simulate card strategies for deck building games?
I admit I don't have much experience in actually doing this, so I have no idea how well any of these actually work and can't make any guarantees myself. But I'm sure there are others who can, and these are probably some great starting points:

dominion simulator python framework

similar project

vdom java simulator

A sourceforge project

Dominionsim is also mentioned here

Here are some I found for Magic: The Gathering. Once again, I can't make any personal guarantees:

MTG Studio (don't know if it actually supports simulations)

Magic Workstation 

If you are anyone else has more feedback on any of these, I'd love to here it!