As far as I know, the think about IAMS doing animal testing is because they were bought by Procter & Gamble a few years ago (1999 ??). I don't think that they do animal testing while they are manufacturing pet food but in other areas (cosmetics, drugs & stuff)..I can't be sure of course
I would never feed my cats with Science Diet. They preserve their food with BHA & BHT, instead of Vitamin C & E, because they are cheaper ! (They are potential 'cancer, liver & kidney disorders' causing chemicals !! ) I am not sure but I think Science Diet dog food (& most other brands of dog food) is preserved with ethoxyquin, which is actually an insecticide, & is not allowed for food for human consumption (except for some spices such as paprika) !
I feed my cats with Eukanuba. I have checked Purina, Science Diet & Nutro's ingredients & I personally think Eukanuba is the best regarding to its ingredients. Yet I will never know if its ingredients were ethoxyquin preserved before even getting to the IAMS factory !!..
... And I have no idea about the ingredients of cat food which are sold only online but not in pet-stores. There are probably high-quality products among those brands ??