PCSM-221. Add test to reproduce pcsm duplicate key error when handling shard key updates

tests/test_collections_sharded.py

@@ -1,4 +1,6 @@
 # pylint: disable=missing-docstring,redefined-outer-name
+import threading
+import time
 from datetime import datetime
 
 import pytest
@@ -85,3 +87,28 @@ def test_create_collection_with_collation_with_shard_key_index_prefix(
         )
 
     t.compare_all_sharded()
+
+@pytest.mark.parametrize("phase", [Runner.Phase.APPLY, Runner.Phase.CLONE])
+def test_shard_key_update_duplicate_key_error(t: Testing, phase: Runner.Phase):
+    """
+    Test to reproduce pcsm duplicate key error when handling shard key updates
+    """
+    db_name = "test_db"
+    collection_name = "test_collection"
+    coll = t.source[db_name][collection_name]
+    t.source.admin.command("shardCollection", f"{db_name}.{collection_name}", key={"key_id": 1})
+    coll.insert_one({"key_id": 0, "name": "item_0", "value": "value_0"})
+    def perform_shard_key_updates():
+        num_updates = 20
+        for i in range(1, num_updates + 1):
+            key_id = 100 + i
+            new_key_id = 5000 + i
+            coll.insert_one({"key_id": key_id, "name": f"test_doc_{i}", "value": f"value_{key_id}"})
+            coll.update_one({"key_id": key_id}, {"$set": {"key_id": new_key_id, "shard_key_updated": True}})
+            time.sleep(0.05)
+    update_thread = threading.Thread(target=perform_shard_key_updates)
+    update_thread.start()
+    with t.run(phase):
+        update_thread.join()
+        time.sleep(5)
+    t.compare_all_sharded()