Where we are weakest is on tests that are driven by UI scripting. I was really impressed with the system we had for that at Asana and I'd like to do something similar in Meteor. But right now our priorities are opening up the package system and doing a round of server scalability work.
I'd like to see what a fully decomposed meteor application is supposed to look like from an architecture perspective but every time I see an example it looks like this.
Testing frameworks force you to break things up resulting in a better overall design. This is what should be exposed to a nascent community if you don't want serious growing pains later on (look at the struggles the php world is having adopting testing and modular architectures)