Make the in-memory kafka writer call unique_key().
So that errors in unique_key() are caught by tests using the in-mem writer.
Migrated from D4621 (view on Phabricator)
Staging instance, all changes can be removed at any time
So that errors in unique_key() are caught by tests using the in-mem writer.
Migrated from D4621 (view on Phabricator)