Save tests are for forward compatibility: import a key in the current format
and check that it has the expected storage format so that future versions
will still be able to read it.
Read tests are for backward compatibility: read a key in the format of a
past version (injected into storage) and check that this version can use it.
Exercise the key unless it is meant to test metadata storage only.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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