I and our other devs have ATi graphics cards. However we have encountered that some shaders that compile without warnings on ATi don't compile at all on nVidia. The problems are trivial to fix, but often go unseen.
My question is, how can I make sure that my shaders will compile everywhere?
Have a bunch of different systems for testing, I can't imagine a way of getting around that.
Optimally you should have a card from every graphics generation.
If you want a really thorough testing you can multiboot all these machines with a bunch of different operating system and driver configurations, but for a more manageable number of tests you can do multiple operating systems and drivers on just one machine each.
Apart from all this, why don't you diversify your dev machines? Maybe you'll also discover more subtle bugs earlier.
Even if you can find a way of testing this exact subtlety there is no way you'll be able to test all the things you should without getting at least one nVidia card.
