We attempted to come up with a similar format for Runscope tests (YAML and all) but quickly abandoned it once we tried anything remotely complex (chained requests, control flow, limits of declarative assertions, etc.). YAML quickly becomes far less expressive than code. I still prefer using a UI like Runscope personally, but I’d use code if it weren’t available.

Also, any proper GraphQL support would abstract away the payload format. It should simulate a GraphQL client, not an HTTP client.