This kind of fuzzing-but-for-correctness is more commonly called property based testing. In that world, the use of a reference implementation as you suggest is

This kind of fuzzing-but-for-correctness is more commonly called property based testing. In that world, the use of a reference implementation as you suggest is often called an "oracle" - and is a good and simple example of a very effective property to test (agreeing with oracle X). Property based testing is not as popular as it should though. But for most programming languages there are decent libraries/frameworks for it, and generally a much more ergonomic choice than using a fuzzing library for this. Most frameworks will do automatic minimization of failure cases, for example. In Python one has Hypothesis as a great implementation. It also has tools for testing stateful code, using a state machine specification.