CSHARP-5723: Add exponential backoff to operation retry loop for server overloaded errors

specifications/client-backpressure/tests/backpressure-connection-checkin.json

@@ -0,0 +1,111 @@
+{
+  "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": [
+          "connectionCheckedOutEvent",
+          "connectionCheckedInEvent"
+        ]
+      }
+    },
+    {
+      "client": {
+        "id": "fail_point_client",
+        "useMultipleMongoses": false
+      }
+    },
+    {
+      "database": {
+        "id": "database",
+        "client": "client",
+        "databaseName": "backpressure-connection-checkin"
+      }
+    },
+    {
+      "collection": {
+        "id": "collection",
+        "database": "database",
+        "collectionName": "coll"
+      }
+    }
+  ],
+  "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": "cmap",
+          "events": [
+            {
+              "connectionCheckedOutEvent": {}
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "connectionCheckedOutEvent": {}
+            },
+            {
+              "connectionCheckedInEvent": {}
+            },
+            {
+              "connectionCheckedOutEvent": {}
+            },
+            {
+              "connectionCheckedInEvent": {}
+            }
+          ]
+        }
+      ]
+    }
+  ]
+}

specifications/client-backpressure/tests/backpressure-connection-checkin.yml

@@ -0,0 +1,60 @@
+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:
+        - connectionCheckedOutEvent
+        - connectionCheckedInEvent
+  - client:
+      id: fail_point_client
+      useMultipleMongoses: false
+  - database:
+      id: database
+      client: client
+      databaseName: backpressure-connection-checkin
+  - collection:
+      id: collection
+      database: database
+      collectionName: coll
+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: cmap
+        events:
+          - connectionCheckedOutEvent: {}
+          - connectionCheckedInEvent: {}
+          - connectionCheckedOutEvent: {}
+          - connectionCheckedInEvent: {}
+          - connectionCheckedOutEvent: {}
+          - connectionCheckedInEvent: {}