Re: pg_basebackup test coverage

On Thu, Dec 10, 2020 at 12:32:52PM -0500, Robert Haas wrote:
> It would probably be good to fix as much of this as we can, but there
> are a couple of cases I think would be particularly good to cover. One
> is 'pg_basebackup -Ft -Xnone -D -', which tries to write the output as
> a single tar file on standard output, injecting the backup_manifest
> file into the tar file instead of writing it out separately as we
> normally would. This case requires special handling in a few places
> and it would be good to check that it actually works. The other is the
> -z or -Z option, which produces a compressed tar file.
>
> Now, there's nothing to prevent us from running commands like this
> from the pg_basebackup tests, but it doesn't seem like we could really
> check anything meaningful. Perhaps we'd notice if the command exited
> non-zero or didn't produce any output, but it would be nice to verify
> that the resulting backups are actually correct. The way to do that
> would seem to be to extract the tar file (and decompress it first, in
> the -z/-Z case) and then run pg_verifybackup on the result and check
> that it passes. However, as far as I can tell there's no guarantee
> that the user has 'tar' or 'gunzip' installed on their system, so I
> don't see a clean way to do this. A short (but perhaps incomplete)
> search didn't turn up similar precedents in the existing tests.
>
> Any ideas?

I would probe for the commands with "tar -cf- anyfile | tar -xf-" and "echo
foo | gzip | gunzip". If those fail, skip any test that relies on an
unavailable command.