It's by far not the first scene done in any ray tracer, rather an early test scene for radiosity (diffuse-only global illumination, before path tracing was developed).
I'd guess the Utah teapot, it's been around since 1975. Cornell box is from 1984, and test scenes for materials are in some way a pretty recent thing, at least how they are used now; to me the modern versions started with Maxwell Render.