Linux 5.12's very bad, double ungood day

I guess if the test setup uses a checksummed filesystem then you verify the filesystem after the tests have completed and if it's corrupted, that's a failure. If the filesystem doesn't have per-file checksums, you can at least do the usual fsck stuff to check metadata. (For testing it would be handy to have a filesystem mode that always zeroes out unused pages, so that a thorough fsck can later check that all unused pages are zero.)