CSHARP-4829: Drivers should unpin connections when ending a session (#1646)

Author: sanych-sun

specifications/load-balancers/tests/transactions.json

@@ -1616,6 +1616,50 @@
           ]
         }
       ]
+    },
+    {
+      "description": "pinned connection is released when session ended",
+      "operations": [
+        {
+          "name": "startTransaction",
+          "object": "session0"
+        },
+        {
+          "name": "insertOne",
+          "object": "collection0",
+          "arguments": {
+            "document": {
+              "x": 1
+            },
+            "session": "session0"
+          }
+        },
+        {
+          "name": "commitTransaction",
+          "object": "session0"
+        },
+        {
+          "name": "endSession",
+          "object": "session0"
+        }
+      ],
+      "expectEvents": [
+        {
+          "client": "client0",
+          "eventType": "cmap",
+          "events": [
+            {
+              "connectionReadyEvent": {}
+            },
+            {
+              "connectionCheckedOutEvent": {}
+            },
+            {
+              "connectionCheckedInEvent": {}
+            }
+          ]
+        }
+      ]
     }
   ]
 }

specifications/load-balancers/tests/transactions.yml

@@ -596,3 +596,21 @@ tests:
           - connectionCheckedOutEvent: {}
           # Events for abortTransaction.
           - connectionCheckedInEvent: {}
+
+  - description: pinned connection is released when session ended
+    operations:
+      - *startTransaction
+      - *transactionalInsert
+      - *commitTransaction
+      - &endSession
+        name: endSession
+        object: *session0
+    expectEvents:
+      - client: *client0
+        eventType: cmap
+        events:
+          # Events for the insert and commitTransaction.
+          - connectionReadyEvent: {}
+          - connectionCheckedOutEvent: {}
+          # Events for endSession.
+          - connectionCheckedInEvent: {}