fix: update coverage test to expect errors for disabled push notifications

- Fix TestConnWithoutPushNotifications to expect errors instead of nil
- Update test to verify error messages contain helpful information
- Add strings import for error message validation
- Maintain consistency with improved developer experience approach

The test now correctly expects errors when trying to register handlers on
connections with disabled push notifications, providing immediate feedback
to developers about configuration issues rather than silent failures.

This aligns with the improved developer experience where VoidProcessor
returns descriptive errors instead of silently ignoring registrations.

Author: ndyakov

push_notification_coverage_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"net"
+	"strings"
 	"testing"
 	"time"
 
@@ -245,20 +246,26 @@ func TestConnWithoutPushNotifications(t *testing.T) {
 		t.Error("VoidPushNotificationProcessor should return nil for all handlers")
 	}
 
-	// Test RegisterPushNotificationHandler returns nil (no error)
+	// Test RegisterPushNotificationHandler returns error when push notifications are disabled
 	err := conn.RegisterPushNotificationHandler("TEST", newTestHandler(func(ctx context.Context, notification []interface{}) bool {
 		return true
 	}), false)
-	if err != nil {
-		t.Errorf("Should return nil error when no processor: %v", err)
+	if err == nil {
+		t.Error("Should return error when trying to register handler on connection with disabled push notifications")
+	}
+	if !strings.Contains(err.Error(), "push notifications are disabled") {
+		t.Errorf("Expected error message about disabled push notifications, got: %v", err)
 	}
 
-	// Test RegisterPushNotificationHandler returns nil (no error)
-	err = conn.RegisterPushNotificationHandler("TEST", newTestHandler(func(ctx context.Context, notification []interface{}) bool {
+	// Test RegisterPushNotificationHandler returns error for second registration too
+	err = conn.RegisterPushNotificationHandler("TEST2", newTestHandler(func(ctx context.Context, notification []interface{}) bool {
 		return true
 	}), false)
-	if err != nil {
-		t.Errorf("Should return nil error when no processor: %v", err)
+	if err == nil {
+		t.Error("Should return error when trying to register handler on connection with disabled push notifications")
+	}
+	if !strings.Contains(err.Error(), "push notifications are disabled") {
+		t.Errorf("Expected error message about disabled push notifications, got: %v", err)
 	}
 }