Attribute expressions

closes #659
Ok. I find test into comprehensive to be a little difficult to use simply because if something breaks I don't know what's breaking where until I step through the loop which could be very large. What I've been doing is basically commenting out the things that I know aren't causing the problem and then test until I get it. This leaves something to be desired. Would the not stopping behavior of parametrize be useful here? It will tell you what the argument types/values are when it falls.