From a6bb7589d989169a54dc2b7c2ca6d3f17e662513 Mon Sep 17 00:00:00 2001
From: Noah Stapp <noah.stapp@mongodb.com>
Date: Tue, 10 Mar 2026 15:02:54 -0400
Subject: [PATCH] Added new test

---
 .../backpressure-connection-checkin.json      | 187 ++++++++++++++++++
 1 file changed, 187 insertions(+)
 create mode 100644 test/client-backpressure/backpressure-connection-checkin.json

diff --git a/test/client-backpressure/backpressure-connection-checkin.json b/test/client-backpressure/backpressure-connection-checkin.json
new file mode 100644
index 000000000..d515c97eb
--- /dev/null
+++ b/test/client-backpressure/backpressure-connection-checkin.json
@@ -0,0 +1,187 @@
+{
+  "description": "tests that connections are returned to the pool on retry attempts for overload errors",
+  "schemaVersion": "1.3",
+  "runOnRequirements": [
+    {
+      "minServerVersion": "4.4",
+      "topologies": [
+        "replicaset",
+        "sharded",
+        "load-balanced"
+      ]
+    }
+  ],
+  "createEntities": [
+    {
+      "client": {
+        "id": "client",
+        "useMultipleMongoses": false,
+        "observeEvents": [
+          "commandStartedEvent",
+          "commandFailedEvent",
+          "connectionCheckedInEvent"
+        ],
+        "ignoreCommandMonitoringEvents": [
+          "killCursors"
+        ]
+      }
+    },
+    {
+      "client": {
+        "id": "fail_point_client",
+        "useMultipleMongoses": false
+      }
+    },
+    {
+      "database": {
+        "id": "database",
+        "client": "client",
+        "databaseName": "retryable-writes-tests"
+      }
+    },
+    {
+      "collection": {
+        "id": "collection",
+        "database": "database",
+        "collectionName": "coll"
+      }
+    }
+  ],
+  "initialData": [
+    {
+      "collectionName": "coll",
+      "databaseName": "retryable-writes-tests",
+      "documents": [
+        {
+          "_id": 1,
+          "x": 11
+        }
+      ]
+    }
+  ],
+  "tests": [
+    {
+      "description": "overload error retry attempts return connections to the pool",
+      "operations": [
+        {
+          "name": "failPoint",
+          "object": "testRunner",
+          "arguments": {
+            "client": "fail_point_client",
+            "failPoint": {
+              "configureFailPoint": "failCommand",
+              "mode": "alwaysOn",
+              "data": {
+                "failCommands": [
+                  "find"
+                ],
+                "errorLabels": [
+                  "RetryableError",
+                  "SystemOverloadedError"
+                ],
+                "errorCode": 2
+              }
+            }
+          }
+        },
+        {
+          "name": "find",
+          "object": "collection",
+          "arguments": {
+            "filter": {}
+          },
+          "expectError": {
+            "isError": true,
+            "isClientError": false
+          }
+        }
+      ],
+      "expectEvents": [
+        {
+          "client": "client",
+          "eventType": "all",
+          "events": [
+            {
+              "commandStartedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "commandFailedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "commandStartedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "commandFailedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "commandStartedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "commandFailedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "commandStartedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "commandFailedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "commandStartedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "commandFailedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "commandStartedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "commandFailedEvent": {
+                "commandName": "find"
+              }
+            },
+            {
+              "connectionCheckedInEvent": {}
+            }
+          ]
+        }
+      ]
+    }
+  ]
+}