The hook checking that no orphaned documents are present on disk at the end of a test works as follows:

• For each shard
  • Run the CheckOrphansAreDeletedHelpers that does the following :
    1. Wait for migration coordinator documents to become zero drain
    2. Wait for range deletion task documents to become zero
    3. Check that no orphans are left on the shard

It has been observed a failure on step (3) because the hook wrongly believed that some documents actually owned by a shard were orphaned.

The reason of the failure was the following: shard1 was migrating data to shard0 and the hook started analyzing shard0:

• Step 1 passed because the migration coordinator is only present on the donor side
• Step 2 passed because the "pending" range deleter task document was removed right after the migration committed
• Step 3 failed because the read from config.chunks did not account for the migration just committed, probably because reading from a secondary node of the config server