Add tests for revision_log_by

#432 (closed) went under the radar because the revision_log_by method is untested. Some simple tests need to be added.

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Migrated from T457 (view on Phabricator)

assigned to @qcampos

marked this issue as related to #432 (closed)

added Storage manager priority:Low labels

mentioned in commit cbaed54c

mentioned in commit swh-objstorage@8501d47d

closed