[evil-olive]

it's rather easy to have both randomness and reproducibility, though:

generate a random seed, log it, then create an RNG using that "random, but recorded" seed. make sure all randomness used in the test flows from that explicitly-seeded RNG.

then, have an escape hatch where if a seed is provided as an environment variable, it will use that instead of generating one.

if you have a failure occur, you can always re-run with the same seed as a way to reproduce the failure (assuming it was indeed caused by that random seed and not some other factor)

depending on how fast the tests are, it may also be possible to run them multiple times with different seeds. for example, your on-every-commit CI run might run once with a hardcoded seed of 42. or it might run once with a hardcoded seed and once with a random seed.

and meanwhile, you might have a nightly test run that runs that same test suite 100 or 1000 times, with a different random seed each time.