You’re pretty much describing LocalStack [1].

IMO much of the product’s success was derived from the extensive snapshot + behavioural tests they created to validate parity with AWS.

The basic engineering loop was: 1. Write tests against AWS 2. Record all results 3. Run tests from (1) against emulator and diff with results from (2)

Like, theoretically, you could use their preexisting suite of tests to construct a pretty decent emulator, since the engineering + cloud costs of recording behavior has already been frontloaded, and resides within their snapshot files [2].

[1] https://github.com/localstack/localstack

[2] https://github.com/localstack/localstack/tree/main/tests/aws...