It was some ad-hoc functions to account for versions, while the already
factored-out serializer just supported the latest version.
Now, we can fold that version-specific logic into the factored out one,
and so we do.
Continue with the characterization testing idioms begun in
c70484454f, but this time for unit tests.
Co-authored-by: Andreas Rammhold <andreas@rammhold.de>