RUBY-3790 new backpressure-connection-checkin spec test

Author: jamis

lib/mongo/session.rb

@@ -458,7 +458,7 @@ def with_transaction(options = nil)
       overload_error_count = 0
       overload_encountered = false
 
-      loop do
+      loop do # rubocop:disable Metrics/BlockLength
         if transaction_attempt > 0
           if overload_encountered
             delay = @client.retry_policy.backoff_delay(overload_error_count)
@@ -539,11 +539,10 @@ def with_transaction(options = nil)
               if deadline_expired?(deadline) ||
                  (e.is_a?(Error::OperationFailure::Family) && e.max_time_ms_expired?)
                 transaction_in_progress = false
-                if @with_transaction_timeout_ms && deadline_expired?(deadline)
-                  make_timeout_error_from(e, 'CSOT timeout expired during withTransaction commit')
-                else
-                  raise
-                end
+
+                raise unless @with_transaction_timeout_ms && deadline_expired?(deadline)
+
+                make_timeout_error_from(e, 'CSOT timeout expired during withTransaction commit')
               end
 
               if e.label?('SystemOverloadedError')
@@ -1401,12 +1400,9 @@ def backoff_would_exceed_deadline?(deadline, backoff_seconds)
     # In CSOT mode raises TimeoutError with last_error's message included as a substring.
     # In non-CSOT mode re-raises last_error directly.
     def make_timeout_error_from(last_error, timeout_message)
-      if @with_transaction_timeout_ms
-        raise Mongo::Error::TimeoutError, "#{timeout_message}: #{last_error}"
-      else
-        raise last_error
-      end
-    end
+      raise Mongo::Error::TimeoutError, "#{timeout_message}: #{last_error}" if @with_transaction_timeout_ms
 
+      raise last_error
+    end
   end
 end

spec/spec_tests/data/client_backpressure/backpressure-connection-checkin.yml

@@ -0,0 +1,67 @@
+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: {}
+          - connectionCheckedOutEvent: {}
+          - connectionCheckedInEvent: {}
+          - connectionCheckedOutEvent: {}
+          - connectionCheckedInEvent: {}
+          - connectionCheckedOutEvent: {}
+          - connectionCheckedInEvent: {}
+