fix monnogo v2 test (#1753)

Author: hellertang

tencentcloud/resource_tc_mongodb_instance.go

@@ -365,9 +365,19 @@ func resourceTencentCloudMongodbInstanceRead(d *schema.ResourceData, meta interf
 	// standby instance list
 	var standbyInsList []map[string]string
 	for _, v := range instance.StandbyInstances {
-		standbyInsList = append(standbyInsList, map[string]string{"standby_instance_id": *v.InstanceId, "standby_instance_region": *v.Region})
+		standbyInsList = append(
+			standbyInsList,
+			map[string]string{
+				"standby_instance_id":     *v.InstanceId,
+				"standby_instance_region": *v.Region,
+			},
+		)
+	}
+
+	// if not standby instance, need set `standby_instance_list`
+	if _, ok := d.GetOk("father_instance_id"); !ok {
+		_ = d.Set("standby_instance_list", standbyInsList)
 	}
-	_ = d.Set("standby_instance_list", standbyInsList)
 
 	tags, _ := tagService.DescribeResourceTags(ctx, "mongodb", "instance", client.Region, instanceId)