To test Earth or Moon gravity, we need to use theoretical model oracles. The post is aligned with the Black Box Software Testing Foundations course (BBST) designed by Rebecca Fiedler, Cem Kaner, and James Bach.
If you are software tester at NASA, you probably have tested application that calculates gravity for Solar System planets. Those calculations are based on theoretical models of gravity. Another example is a software tester of an app that calculates pipe pressure on oil rigs.
Some theories are experimentally well tested. An example is the speed of sound on Earth.
Some theories are only approximation of the real world. Newton and Einstein created different gravity theory. Former hold on Earth and later is for space travel.