[Test only issue]

Problem

In the ContinuousAddRemoveShard hook, after removing a shard, we decommission it, including a final sanity check validating all collections on the shard are empty.

However this check always passes due to misuse of pymongo, there are at least 4 issues:

• In this line we run listCollections on a DB literally called "db_name", not the one referenced by the db_name variable.
• listCollections returns a dict {ok:1, cursor: ..., ...}. In this line we are iterating over the dict keys ("ok", "cursor", ...), not the collection names.

• In this line similarly we run find on a collection literally called "coll", not the one referenced by the coll variable.
• listCollections may return multiple batches but we never iterate them.

The attached repro demonstrates a shard with non-empty collections is not detected by the hook.

Proposed solution

Fix and test the hook code, and create tickets for any issues the fixed code may find.