Add heartbeat implementation to test writer

Author: endigma

v2/pkg/engine/resolve/event_loop_test.go

@@ -51,7 +51,11 @@ func (f *FakeSubscriptionWriter) Complete() {
 	f.messageCountOnComplete = len(f.writtenMessages)
 }
 
+// Heartbeat writes directly to the writtenMessages slice, as the real implementations implicitly flush
 func (f *FakeSubscriptionWriter) Heartbeat() error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.writtenMessages = append(f.writtenMessages, string("heartbeat"))
 	return nil
 }
 

v2/pkg/engine/resolve/resolve_test.go

@@ -4778,6 +4778,9 @@ func (s *SubscriptionRecorder) Complete() {
 }
 
 func (s *SubscriptionRecorder) Heartbeat() error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	s.messages = append(s.messages, "heartbeat")
 	return nil
 }