Add test assertions to verify that the related change fixes usync diff
stats being erroneously incremented as a side-effect of syncing shard
ranges when the object tables are in sync.
Related-Change: I2630bb127841837b35e7786b59895fa50090719b
Change-Id: Idffe93c63d16e74ea9ca42b33a636c0c0d9e35b5