- pg_regress, which is as you say a set of SQL scripts run on a running server with generated output compared to the expected output. There could be multiple expected outputs, see for example float tests.

- pg_isolation_test, which is a part you are misunderstanding. This facility has been introduced with SSI (serializable transactions) to test concurrency.

- TAP tests (author of the replication/backup/recovery part here), which has roughly three test suites:

-- src/bin/ to test all the in-core binaries

-- src/test/ssl to test SSL configurations. This has proved to be useful lately when moving all the SSL parameters to be reloadable.

-- src/test/recovery to test all the kind of replication scenarios.

There are as well modules in src/test/modules that use TAP tests to run regressions on pg_dump, commit timestamps and extension interactions.

Are there, in fact, no tests on VACUUM and others? Is that a problem? Are there plans to add them? Would you be looking for contributors to do so?

diff $(sort output) $(sort expected)