Every place I've ever worked which tried this has managed to get a production database deleted by somebody running tests.
Why not?
But, the one important thing is, do not give people direct access to production. And for the few that must have it, it should not be easy to connect to it.
That's just a different way of saying "Every place I've ever worked at use production for testing" :-/
TBH, any place using the same credentials for test and for production have bigger problems than would ever be fixed by mocking.
... is that good? Hell no. But it's a much more common version of reality than you're assuming is happening.
Sure I've made an assumption, but in my defence it's a single reasonable assumption: that one wouldn't be running tests in production.
If you have a leftover `.env` that contains production credentials, you were running your test in production.
Anyway, the missed point is that you can’t just do anything in tests and just expect the best of intentions to ensure it doesn’t backfire. One must also consider the security situation, infrastructure, secrets management, shared environments, and more. It’s not as simple as just plopping down a test database and expecting everything to go smoothly. You wouldn’t be that careless with other things, so don’t do it with tests, and don’t rely on “don’t run tests in production” as your only safeguard.
Generally I've seen a new database (schema in other dbs?) in postgres that is for testing, i.e "development_test" vs "development". The big thing is to wrap each of your tests in a transaction which gets rolled back after each test.
> maintain this, eg have good, representative testing data lying around
This is much harder. Maintaining good seed data - data that covers all the edge cases - is a large amount of work. It's generally easier to leave it up to each test to setup data specific to their test case, generalizing that data when possible (i.e if you're testing login endpoints, you have all your login test cases inherit from some logic specific data setup, and they can tweak as needed from there). You will end up with duplicated test setup logic. It's not that bad, and often you don't really want to DRY this data anyways.
That being said, if you have the time and resources to maintain seed data it's absolutely a better way to go about it. It's also beneficial outside of tests.