In terms of QFT in curved spacetime (qftics), are there any known tests that confirm/void it to be a correct prescription for a first order approximation quantum theory of gravity? Obviously the extension makes some sense but how is it confirmed?
I know there are a lot of tests including Lorentz violation in qft, ultimately a possible search route to test qftics, but if there are more specific cases this would be extremely useful to know about.